Step up your game, guys.
Speedwagon from
JoJo's Bizarre Adventure.
He used to be a ruffian roaming the streets of London, robbing the people who were unfortunate enough to be in the wrong place, at the wrong time. One day, he happened to meet one man, who quickly disposed of his accomplices and proceeded to knock him down with a swift kick, after showing Speedwagon that he was willing to risk a few wounds because he had come for his father. Then Speedwagon noticed one thing. The man held back. Speedwagon, having asked why, he got the answer from the man that he was thinking of the possibility that Speedwagon have a family. Touched by such kindness, he decided to follow the man, named Jonathan Joestar. And he did his best to help him, like helping Jonathan to unveil the plot of Jonathan's enemy, Dio Brando, then find Dio's location after that awry incident that led to the death of Jonathan's father and the destruction of the Joestar estate. Etc...
His loyalty extended well beyond the eventual death of Jonathan to reach Jonathan's descendants. Just to say so much about his loyalty, he never tried to court Jonathan's wife, and now widow, Erina, née Pendleton, Joestar, even tho the temptation might have been here.
His final fate, I will let the people who are discovering the franchise to find out.
More "Best friends" later.