Nine times out of ten, the borrowed word "bitch" in Japanese gets translated to "bitch" in English, even though Japanese people use it to refer to a sexually promiscuous woman rather than one with a mean disposition.
I just started laughing out loud in the middle of this chapter because I thought, "it'd be funny if the series ended because the MC died during the atmospheric entry."
I probably should've included a TL note on the first page, but the reason Morita is commenting about being the senpai is probably that he's using polite speech with Kurokawa, while Kurokawa is using causal speech.
@LordoftheKeep The closest I know of is in France where anyone from friends to family may kiss each cheek (or kiss the air on both sides of each others' faces, at least) as a greeting, "la bise."