Baku

–Cows jump over the moon. Dragons, they do more than that! Detective Nathaniel Luna fights for the scales of justice during the day. But at night, he develops tougher scales of his own, as he turns into the Bakunawa, a dragon in Southeast Asian folklore, who swallows the moon during a lunar eclipse.
–Baku's power varies, and grows depending on each state of the moon. But he peaks every time he swallows the celestial body, borrowing its power to protect the night during its darkest. But as powerful as Baku is, he was, in the past, merely Nathaniel.
–Back when he was a mortal, his first task upon being promoted to detective was to investigate a tip about the local orphanage. It's owned as a money laundering front by Ice Pick, one of the biggest mafia bosses in town. And he was planning to burn it for insurance money.
–Nathaniel was tasked to stand by across the street during the night of burning. But his backup encountered an unexpected detour. He knew they were gonna be late, and the kids will never make it. So he fired his gun twice to distract, snuck inside, and woke them all up. Just as the last kid got out, Ice Pick's right hand man caught him. And he and his boys had Nathaniel beaten, to death.
–Nathaniel's body was thrown in the river, under a lunar eclipse. And the first incarnation of Bakunawa, the first mooneater, happened to witness all the good that he did for those kids.
–The dragon had always been looking for a new successor, knowing that they were getting old. So they salvaged Nathaniel from the river, and used all their power to bring him back to life.
–The Bakunawa transferred all their essence, knowledge, and abilities to the young man. And from that moment on, Nathaniel took the beast's name as his moniker, taking down the ill-hearted and giving second chances to the better ones.
–That's where you come in. After double crossing Ice Pick, you know you're almost done for. Luckily, Baku knows it too. He tracks you down, follows you home. The next thing you know, a dragon lands on your rooftop in the middle of the night as you were trying to get some fresh air. It shrinks, and turns to a face you've only seen on the news.