As Sirius stares into his best friend, his brother, his Prongs's lifeless hazel eyes, he feels nothing but earth-shattering despair and guilt. As he screams and begs for his friend to wake up, he knows it's because of him that all this came about. The man he used to share jokes with, to laugh with, and to have serious, heartfelt conversations with is gone. He takes James's hand and holds it within his own, and he knows his hazel eyes will never sparkle, never shine with mischief, never stare at Lily with that all-encompassing love again. His best friend is no more.
He is going to kill that little rat Wormtail; he's going to destroy the vermin that tore his entire life into pieces. Pettigrew had him firmly believing that Remus was the spy; he kept posing questions to him, kept saying, "Hasn't Moony been acting oddly lately, Padfoot?" trying to take the blame off himself. As Sirius keeps staring at James, whose eyes are still wide open and staring, he vows that he's going to have vengeance on the moronic little rat. Peter, who struggled just to get through school, who ruined some of the Marauders' pranks, has pulled the biggest prank of them all.
The look on his brother's face is heartbreaking to behold. He looks terrified but determined to fight for his family, and Sirius takes the man in his arms, holding him close and whispering how sorry he is over and over again. He remembers that the last time they said goodbye, James hugged him tightly and said, "Stay strong, Pads. Everything will be all right, the war'll be over before you know it, and Lily, Harry, and I can come out of hiding." Even at that time, Sirius couldn't help but feel that that was the beginning of James's doom, that that would be the last time they'd ever see each other.
Sirius sees another set of lifeless eyes when he comes across Lily. The beautiful woman, who was so vibrant and full of life, has a look of pleading in her open green eyes. It's almost as if she's begging Sirius for help, and Sirius collapses by her in guilt, knowing that he was unable to do anything for her. Her hand is still soft and smooth, but it's so stiff and cold. "I love you and I'm so, so sorry," he whispers, holding Lily close just as he did James.
He carries her to where James is and puts her down beside him, closing the couple's eyes for them. James still does not look peaceful, though, and neither does Lily. A howl emanates from Sirius's throat, a howl of despair and sorrow. All is lost, his entire family is gone. His blood family, he doesn't give a rat's ass about; James, Lily, Harry, Remus, and Peter were his real family. Remus will hate him now, thinking it's his fault, and Peter ... Peter was the real Secret-Keeper, and the miserable little parasite betrayed two of the dearest people he has ever known.
He can't believe his eyes when Peter gets the better of him and screams, "Lily and James, Sirius! How could you?" right in the middle of the street. A lightning bolt of anger shoots through Sirius, and he has nothing but revenge and murder in his heart as he points his wand at Peter. The boy who used to raid the kitchens is now forever gone as Peter gives him a tiny, but malicious smirk.
Suddenly, the street goes kaboom! and blows up, sending bodies and debris flying everywhere. Sirius gazes at the scene for a moment, unable to comprehend what has just happened, and then he begins to laugh, a mirthless, raucous cackle which can be heard from miles away. His entire stomach hurts from laughing so hard, and he thinks, inept little Peter Pettigrew got the best of smart, clever Sirius Black! He sees the little rat disappear into the sewers, and he knows that now he is the one people will definitely blame.
As the door to his Azkaban cell slams, Sirius starts to weep. Tears of anger, of helplessness, of hopelessness, of loss, of misery stream down his face, and great, racking sobs seize his body. He has fallen into a black abyss, a great well of despair. James's lifeless eyes haunt his mind, and Lily's look of pleading sends him into hysteria. Harry is God-knows-where, and he's eventually going to hear that his godfather killed his beloved parents.
And for twelve years, Sirius rots in the cell. Turning into Padfoot is only a slight comfort, and so is the thought that he is innocent. The dementors thrive on his worst memories, and Sirius can still smell the choking smoke and see the fallen beam that is on top of the body of his brother, his best friend, his everything. The rattling breaths of the foul beasts make him sob in absolute anguish and agony.
But then, one day, Cornelius Fudge comes to inspect the prison. In his hand is a newspaper, and when Sirius asks for it, he sees that evil little Peter Pettigrew is on the cover. He has to get out of there, he decides. Peter's going to be at Hogwarts, with Harry, and he is again haunted by lifeless eyes, this time belonging to his precious godson. He can't let that be a reality.
When he finally escapes, he can't believe he's accomplished such a feat. He travels to Hogwarts, and he is tired and weak, but he knows he must get there quickly. Memories of James still consume him, and he wonders if Remus is still alive. Oh, sweet and gentle Remus. How could he ever have suspected him of betrayal?
When he arrives at Hogwarts and sees Harry playing Quidditch, complete nostalgia burns inside him. He can remember James flying, and the crowd whooping and cheering. But as well as the sadness, a ray of hope blooms inside him. He's going to do right by Harry now; he's going to let him know the truth, whatever it takes. He knows the guilt of James and Lily's deaths will never go away, and it's their eyes that will haunt him the most. But he also knows that there's a living reminder of them in the world, and he's going to do his best and show his godson unconditional love. I love you, little Prongslet, he thinks as he continues to watch him soar above the sky.