When Rin starts visiting the academy, Lewin is 100% a little shit as a teacher. And Rin exclusively calls him "Mr. Light" just to get on his nerves. It’s basically a Cold War Competition to see who can crack on being passive-aggressive to each other first(usually the winner was Rin because of sheer stubbornness, but Lewin had his moments).

Although, Lewin talks about Rin all the time when he’s alone with Ryuji and he shows off all kinds of embarrassing photos from when Rin was little.

Ryuji once asked how Lewin managed to raise a kid, and the Son of Satan no less, and Lewin just shrugged(He’s messing with Ryuji at this point because he totally reverse psychology’d Rin through childhood. But Lewin prides himself on being a decent parent because the freedom he gave Rin allowed for a hella independent and sassy child and Lewin couldn’t be more proud.)