Well, I have no idea what to say expect this ought to be fun. Welcome to my Harry Potter/Build crossover, this one was suggested by MaryamSahibzada, who suggested that I do a HP/Build story with Miss Ginevra Molly Weasley as the lead, where she meets Sento and well, here it is. I honestly had no idea how to do this but I am going to treat the two franchises that will be in this story as separate worlds, cause in my head, I see all my favorite franchises being in one world, unless stated otherwise. So yeah, HP and Build are their own worlds.

Summary: Ginny Weasley is sent to another world and becomes the aid to the amnesic Sento Kiryu to help him fight against the Smashes and regain his lost memories. As she tries to help him, Ginny finds herself involved with the war between the three nations of Japan and finding help from a convicted prisoner and a strange man with his strange daughter. Can she find her way back to her world? Or is she stuck in this strange world ?

Pairings: We'll see what happens

Disclaimer: I own none of this, Harry Potter belongs to J. K. Rowling and Bloomsbury Publishing, Kamen Rider Build is owned by Toei TV and Shotaro Ishinomori. If I had owned anything of this, I have no idea where I would change.

Best Match: Magic and Chemistry

Chapter 1 - The One with the Best Match

The rain was pouring hard and aside from the pitter-patter of the rain on his umbrella and the various items around the alleyway, the alleyway was quiet. A barista, wearing a green hat which hid his black hair and round sunglasses on his nose to cover his brown eyes, looked around after he had taken in a young man with no memory of his past, he had explained to his daughter that he was taking a second look around the area in case he had forgotten something. He wondered if he would find anything or thought that there was anything left to find the alleyway.

Hearing a soft moan, the barista listened and walked around, looking for the source of the moan. He looked around, walking a few steps and looked, gasping as he saw the source of the moan and couldn't believe what he had seen.

Finding a clean blanket, he wrapped it around the person he had found and carried the unconscious person back to his coffee shop, nascita. Luckily, there were no customers so he didn't need to worry about concerned look as he carried the person into the shop and behind the counter, walking to a small fridge hidden in the back of the shop. He opened the door and knelt down, going down a spiral staircase and saw his daughter, who had black hair in a up do and brown eyes in a white dress, look up from watching the strange black haired young man on the bed.

"Who is that, dad?" She asked, looking at him. He smiled, "Another member of our ever growing family." He carefully laid the person on the bed next to the young man, and revealed it was a young woman with long flaming red hair, her face covered in a dusting of freckles, wearing a school uniform of some kind and was breathing soundly like the man. The older man covered his mouth and hid a smile, thinking about what to do with this girl.

-A Year Later-

Ever since that day, the two had stayed hidden in the basement of nascita, helping each other, the girl helping the boy regain his lost memories due to her having all her memories expect when she had arrived in the city whereas he did not. And they also became friends with the two residents of the coffee shop, the owner, Soichi Isurugi, and his daughter, Misora Isurugi as well becoming friends with each others.

Despite how long they had helped each other, the girl thought she had growing feelings for the boy she shared the basement with, but she doubted that he felt the same since he was busy with inventions and she thought that he reminded her of a annoying school bully from her old school. When it came to outfits to wear, the girl revealed that she could do magic and change her clothes into something more suitable though she was also a small wardrobe to wear though she kept the robe and necktie she wore as is.

Another unique thing about the girl was that she spoke, the three learned that she was British and could only speak English, thus began to teach her to speak Japanese. Within no time, she began to speak fluent Japanese and did her best to help her new friends and family. At some point, she bore witness to the boy getting a unique belt and a few small bottles, the boy being asked to use them for heroic purposes and that she support and help him in anyway.

As she learned to speak the language, there was another thing the girl learned about where she was. 10 years prior, there was a incident known as the Sky Wall Incident during which a wall appeared and separated Japan into three country, Hokuto, the northern country which dealt with social welfare, Seito, the southern western country that worked with economic recovery, and Touto, the eastern country which practiced traditional pacifism and was where the cafe was located.

As she finished putting her flaming red hair into a braid, the girl looked at her reflection, noting how much she had grown within the past year, her brown eyes looking at her reflection. Her face covered in a dusting of freckles, her long red hair braided back into a ponytail, she wore a gray short sleeved shirt that exposed her shoulders with the red and gold necktie wrapped around her right bicep while she wore around a white asymmetric skirt with tan leggings and brown slip-on trainers on her feet. She grabbed the robe which had been changed into a black overcoat, the house crest had become a patch on the sleeve.

Upon hearing a gasp, the girl left the curtain covered area of the lab that was labeled 'Changing Room' and headed to the part of the room which had two beds and a work area, seeing her companion sitting at the desk as the toaster popped up with his breakfast. She asked, "Sento, are you okay?"

Sento turned to look at her and she was speechless as his face was covered in marker doodles, he said, "Yeah, I'm fine, Gin-chan. Just a bad dream and a bad memory." "Uh, Sento, your face..." Ginny pointed to which he looked at a mirror and saw what had happened to his face. He groaned, "This sucks!" Ginny laughed and dampened a towel to clean his face as he ate a piece of toast and there was a ding as a microwave door opened with smoke coming out. Sento smiled and went over to check the results, grabbing a small white bottle with a black top and bottom.

Ginny sighed as he messed with his hair and said, "Awesome!" She didn't look as a tuft of his hair stood up and the door of the large machine next to it opened, revealing a tired looking Misora as she rubbed her gold bracelet. Sento attempted to give her a hi-five as he said, "Good job!" But she ignored it and walked past him, Ginny asked, "Is that from the monster that you fought last night?" "Yup." Sento said, smiling and showed her the bottle. Then he looked to Misora and asked, "What is this? A hedgehog?" "Don't know..." Misora said, tired and leaning against a pillar. "Don't care. Tired. Want my pay. Sleepy."

Smiling, Ginny finished dampening the towel and Sento said, excited, "What techniques will this have?!" "Sento, how bout we clean up your face first, okay?" Ginny said, walking to him and wiping his face of the marker doodles. Once she was done, Sento smiled and said, "Thanks, Gin-chan. I can't wait to try it!" Ginny shook her head, smiling as she cleaned the towel and hung it to dry.

"But you know, Gin-chan." Sento said, walking over to the machine. "My inventions really are the greatest." "I know, I know." Ginny said, smiling. Sento continued, "With just a few components from the monster, I can create power-up items for Build to use! Of course it's thanks to the strange power that Misora has. But it's all due to my abilities that I can take it to max-" But they saw that Misora had fallen asleep on his bed and Ginny sweatdropped as he got a smile, "Now then."

After a few minutes, the two put on their overcoats and headed up the stairs, Sento having a small smile on his face as he ate the other piece of toast. Soichi came in from sweeping the front of the cafe and looked as Ginny and Sento came out of the secret fridge in the back. As they walked, they jumped and held each other in shock as Soichi appeared, jumping from the other side of the counter. "Buongiorno, Sento-kun! Ginny-chan!" "Soichi-san..." Ginny said, catching her breath as she and Sento let go of each other, Sento said, "You surprised us!" He looked and showed him the bottle, "Here! Results from yesterday."

Taking the bottle and examining it, he smiled and said, looking down at the secret fridge, "Bravo! My dear child! Thank you!" As they sat at the counter, Soichi looked at Sento and asked, "So? Did you remember anything?" "What?" Sento asked, Soichi sighed and said, "Your memory! The twenty-odd years of me-mo-ry you're missing." Ginny laughed and looked at him, Sento thought and said, "A scientist with a gas mask, human testing, and a bat man." But then he sighed, having nothing else to say, Soichi said, "No progress then?"

Ginny touched Sento's shoulder to calm him and he touched her hand, Soichi said, "You created Build to search for that bat man!" Sento sighed and said, "Even when I change the people turned into Smash back to normal, I don't remember anything." Ginny looked down with him as they kept quiet, Soichi interrupted their moment as he said, "And by the way, you've racked up a year's worth of rent." "Wait, when you were renting the basement to us?!" Ginny asked as Sento looked over the checks and said, "What rent?! You were charging us?!" "Of course it does!" Soichi said, smiling at them. "I'm not softhearted enough to let a amnesiac and homeless girl stay free of charge."

"Is that why you made me get a job at the Institute?" Sento said, looking shocked. Soichi said, "It's your first day, isn't it? Should you be lazing about?" Sento looked at his watch and gasped, "Oh crap!" He got off his chair and went to the door but turned around and said, "So when you're in a hurry, you should use..." He revealed his new inventions, "This!" He revealed a cellphone and a yellow bottle, Soichi asked, "What is that? You gonna call in sick?"

"Yeah!" Sento said, putting the phone to his ear but stopped. "Of course not! It's my invention!" "What does it do?" Ginny asked, looking curious. Sento put the bottle into a indent on the side and tossed the phone in the air, hearing something, 'Build Change!' and a motorcycle appeared, Ginny and Soichi were impressed and awed, Sento smiled, "Right?! It's amazing!" "It's fantastic!" Soichi said, Ginny nodded, "It's wonderful." "Indeed, it's genius!" Soichi said as Sento pressed on a touch screen and a helmet appeared, then he mounted the motorcycle, ready to go til the three of them realized something.

"Sento, you idiot!" Ginny said, hitting him with her fist. "You demonstrated inside the cafe!" Soichi laughed and the motorcycle was moved outside, Ginny gave him a tight hug before he left and she waved at him. She hesitantly lowered her hand and breathed, heading back into the cafe and went into the basement lab. She sat at the computer in the lab and watched the news report of the jailbreak of Ryuuga Banjo who had been sentenced to ten years of jail for a crime that he had committed.

She looked at the footage of Ryuga supposedly defeating the guards that were after him, she thought, 'Could he really do that? Sento, be careful...' Soichi and Misora joined her at the computer and looked at the footage, contacting Sento, Soichi said, "Ryuga Banjo. A former martial artist. He was given a perma-ban for fixing games and sentenced to ten years of hard labor for killing a scientist a year ago. The sensor is responding, but there aren't any eyewitness reports of a monster. He might not have become a Smash yet. I hacked into the GPS of the motorcycle Banjo stole, so I'll send you the data."

Ginny got up and ran upstairs to a quad bike she had gotten from Soichi, putting her helmet and going after Sento. Following the direction that Soichi gave her, Ginny arrived where Sento was and saw him shake a blue and red bottle, a unique looking belt around his belt, then turned the taps before inserting them into the belt, with the announcement, "Rabbit! Tank! Best Match!" He suddenly grabbed the level and spun it, starting it slow then went faster.

As a building kit appeared around him, the half in front of him being red and the half behind being blue, it asked, "Are you ready?!" "Transform!" Sento shouted, then the two halves came together on him, giving him the blue and red armor, announcing, "Steel Moonsault. Rabbit Tank! Yeah!" "Go... Sento..." She said, softly, watching him face against the Smash that was in front of him and saw Ryuuga in dirty white clothes, bewildered.

She watched as a drill-shaped sword appeared from his belt and slashed at the Smash. Ginny noted that he removed the Rabbit bottle and brought the Hedgehog bottle, inserting it and spun the lever. "Build up!" He said, as the red become white with spikes. Ginny looked surprised and thought, 'So, there can be more than one Best Match with certain FullBottles.' She looked, watching the fight as he used the new bottle to fight.

Using the abilities of the new bottle, like the fist it gave with the spikes, Sento sent it back and shook a red bottle, saying, "I'll finish you with this." He went back to Rabbit Tank and spun the lever of the belt, before going, "Wait a sec." He ran a distance from the Smash then jumped into the ground as a white chart appeared with the dotted line trapping the Smash. Then Sento jumped and slid along the dotted line, destroying the Smash.

Ginny watched him take a empty bottle and used it to gather the essence of the Smash to reveal the unconscious human who was on the ground. He seemed to notice her and looked at her, realizing that she had been noticed, Ginny ran to Sento and looked at the young man who was once the Smash and he had no idea where he was, Ryuga looked at Sento and said, "It's true! They did something to both of us!" Ginny and Sento kept quiet, since they weren't sure what to say. Ginny looked at Sento as Ryuga grabbed his shoulders, "Believe me!"

"If what you say is true," Sento said. "Then that was the Smash's human experimentation..." Ginny gasped, looking at him. Suddenly the guards appeared and Ginny hid behind him as one of the windows of the car rolled and a voice asked, "So you're the Kamen Rider?" Appearing was a bearded man in a gray uniform, "I heard about you. We'd appreciate it if you'd hand over the murderer Ryuga Banjo." "I didn't kill anyone!" Ryuga shouted.

The man clapped his hands and all the guns were pointed at Ryuga, he sobbed, "I am a worthless piece of idiot garage... but I would never kill anyone. Why... why won't anyone believe me?!" Seeing how quiet he was, Ginny asked, "Sento?" He sighed and knelt down, "This sucks!" Giny and Ryuga looked at him as he said, "I'm totally gonna regret this later." He summoned his motorcycle and told Ryuga, "Get on!" He nodded at Ginny and she went to her quad bike, getting on it then followed after Sento.

Quickly they were followed and Ginny gasped, trying to drive straight as they were shot at and had rockets shot at them, she shouted, "They're crazy!" As they rode up a ramp on the Sky Wall, then rode down on the side, Ginny thought, 'Strike that, Sento's crazy!' Luckily Sento caught her and Ryuga as he used his sword as a brake, his motorcycle stopping her quad bike to land before becoming a phone and landing perfectly while the last pursuer fell to the ground. Once the three were on the ground, they rode off to the nascita.

"Damn, now I'm a fugitive, too." Sento grumbled, Ryuga asked him, "Why did you save me?" "I believe you." Sento said, as Ginny looked at him. "That's all." Then he added, "A real idiot doesn't call himself an idiot. You're not a liar." He gave a chuckle, "Although your fly is open." Ginny looked away, as Ryuga noticed and said, "Since when?!" "Since the beginning." Sento said, Ryuga whined, "Why didn't you tell me?!" "The timing wasn't right." Sento told him. "Figure it out for yourself, idiot."

Ginny just smiled, riding along side him as Ryuga shook him, trying to tell him that he wasn't a idiot. None of them knew of the black bat figured that watched them before disappearing.

And so the story begins, oh I can't wait til Ginny gets the funnier part of the story with Gentoku being a weird silent man and witnessing Kazumi being a otaku fanboy over Misora's Mii-tan idol persona. Well, gonna have to wait and see.

Next chapter, Sento's role as Kamen Rider is now considered a wanted criminal, Ryuga tries to retrace his step about his arrest, Ginny worries about Sento getting caught, the group thinks Ryuga has been framed. This has been WhiteRose-Aki, see you in the next chapter. Please R&R if you enjoyed.