Responses
It's a joke from the high school he's teaching in. They all called him tht for jokes. And since he's a pretty chill teacher he doesn't really do anything abt it except say "dotn call me tht". Read the prequel for more details. It's called "brothers"
I actually thought "Christine" was a translated mistake :D But he's calling him that even in older chapters... really odd :D It's a name mainly a bit older women have in my country xD my older neighbour has that name... please guys, call him Watanabe or just Chris ^^ I don't want to picture my older neighbour each time :P