Responses
I don't think the author sacrificed character consistency. His character simply grew. From the first page, we're told he avoids conflict and serious relationships. Even so, he couldn't ignore the injured man that the yakuza left on the road to die. To stay safe, he took him to a hotel instead of a hospital and treated his wounds. After that, he tried to stay away, but he was still worried enough to come back.
He's still the same person. He lied that Rei is a foreigner to avoid issues, but he made a better choice and decided to take him home and care for him. That's character development. ;)
Ok but as someone who doesn’t wanna deal with dirty stuff, he picked up a dirty injured guy lol. His personality contradicts his previous actions. I can see that author sacrificed character consistency in order to remain faithful to the story they envisioned (which was: guy picks up homeless dude but doesn’t want to deal with him, rei’s persistence, doctor’s regret, then happy reunion). It’s a straightforward plot.