[@Vulkan] I'm gonna go with this, they talk to each other via Steam chat and even though its not his preferred method of interaction, Kiyoshi likes Takuma enough to tolerate it with him, but would still be a hard ass to at least get him to know some basic signs for the quick and easy stuff.

just like, "Ok, guy...we've known each other for a while now and we've communicated really well...but this chat bs is getting old real quick and that shit won't fly in class, so if we're gonna keep hanging out, you're gonna learn SOME sign language."