Kakashi wanders the ruins
Kakashi, decidedly, did not stay put.
As much as Toriel seemed to worry about his well being, most of it was completely unfounded. The so called 'dangerous' puzzles certainly weren't a threat, and neither were the unorthodox so called 'monsters'.
The only real threat, besides potentially the goat lady herself (which could only become a problem from her own instability rather any intent to harm him), was that flower with the stupidly un-ironic name.
'That thing rubs me in all the wrong ways,' Kakashi thought as he started to take a handful of candies from a glass bowl sitting on one of the many random pillars that never seemed to connect to anything other than the floor.
'You monster, the sign says take one,' he heard Obito say.
Kakashi checked over the candies. They had no label, just the multicolored wrappings. He drew one up close to his face and took a large whiff of the smell. They were sweet, sweeter than most deserts he had ever smelled and most likely packed with the monster equivalent of sugar. Then again, appearances can be deceiving.
To quick for the eye to see, Kakashi pulled down his mask and took a tiny lick. To his surprise, the candy dissolved almost instantly against his tongue, filling his taste buds with the unfamiliar, but still quite enjoyable taste.
Even more surprising, was how it effected his ankle. Though mostly healed by Kakashi's emergency medical ninjutsu, it was still stiff, and he only kept himself from limping by steadily supplying chakra to that area. That was, until the candy somehow almost completely healed it.
Curious, Kakashi popped what was left of the candy into his mouth, and he felt almost reinvigorated. gone was the lingering tiredness from staying up all night for days on end to reach the land of earth from Konoha as quickly as possible.
He decided that he must bring some of these home so that they could be studied and replicated. Imagine being able to heal wounds on a battlefield with just a single candy! It even tasted good unlike the standard issue soldier pills.
With that happy thought, Kakashi sealed his handful into a scroll that his then put into his pack for safe keeping and resumed his trek across the ruins.
Despite the many warnings from the goat lady that the ruins were a confusing place, Kakashi didn't find them all that complex. Though there were many nooks and crannies that strayed from the main path, there was a clear path that was meant to be followed, most likely leading to wherever Toriel lived, and it was only barred by easily solvable puzzles. Most of them didn't even go beyond flipping a switch or two.
Really, the hardest part was dealing with overzealous monsters who occasionally attacked him with strange, easily avoidable white justsu. He would have to observe it with his sharingan at some point to see if it was able to be mimicked.
Eventually, Kakashi started walking on the ceiling just to avoid these encounters. Even the monsters that could fly stayed close to the ground.
The ceiling was even more infested by vines than the ground. If Kakashi couldn't just walk on the ceiling, he could get by swinging from vine to vine with only the occasional gap that was to far to reach.
After a while traveling like this, Kakashi arrived at one of the larger clearings. There was a black tree in the middle with the path driving directly through it. It was completely depraved of leaves, and the base was covered by a thick layer of autumn red leaves that could have only fallen from the tree. At the end of the clearing was a door leading into an obviously important part of the ruins what with the large, illegible sign mounted above the doorway.
Kakashi could hear sounds walking and clinking kitchenware from inside, and the entire area was surrounded with the ubiquitous smell of cinnamon and butterscotch.
Kakashi dropped down from the ceiling and walked through the door to find... a house?
It was a quaint, homely place, cleaned and tided with love and care. It didn't seem to fit with the dirty, crumbling stones of the ruins infested with vines and littered with crumbling remains of walls and pillars.
Kakashi followed the smell of cinnamon and butterscotch through an equally tidy living room with a cushy chair, fireplace, and bookshelf, as well as a large table in the other corner for eating, and into a kitchen where the goat lady Toriel was taking a monumentally large pie out of the oven. Kakashi was surprised that the pan even fit through the oven door.
She placed the pie on a counter-top to dry while humming a tune Kakashi couldn't recognize before turning around to find the shinobi watching from behind.
"BLEAAAAH," she yelling out indignantly in surprise. It half sounded like the bleating of a distressed goat and half like a regular scream from a human. Kakashi gave her an eye-smile to show his amusement.
"I-I'm terribly sorry my child," she shuddered apologetically, "you took me by surprise."
"I see that you've made pie," Kakashi spoke. Toriel seemed surprised to hear him talk, putting her hand over her mouth before putting them down just as quickly.
"Yes, I was planning on surprising you, my child, but it looks like the opposite ended up happening," she said, letting out a nervous laugh at the end.
"uh-huh," he replied, glancing at the pie and then back at her. "You wouldn't happen to know where the exit is, would you?"
I can't really think of anything good to put as an after note here. I haven't come up with much lore other than what I've already expained, but I would love to hear people's ideas.
I'm telling you all right now that there is no way that Kakashi will get the pacifist ending, but I do want to change it up a bit from the neutral ending. The biggest thing is that Kakashi has a one track attitude. The only thing on his mind is to find out all useful information on the Underground and report back to Konoha. He doesn't know how to cross the barrier, but once he figures it out (which won't be that hard considering all the info on it in the underground) he won't hesitate to kill Asgore for his SOUL.
Right now, I only have one more chapter written, and it is already out on ao3. I'm trying to think of a good way for the Toriel fight to go and how Kakashi and Sans will react to each other. I imagine that once they're done figuring out if they should kill one another, Kakashi can probably learn some bad habits from the skeleton that may or may not reflect in his personality during the Naruto cannon, but right now he's still a baby Kakashi that has not quite learned the true art of being a troll. I don't think he's even started reading porn yet!