Not trying to disparage the translators, but they really didn't capture the MC's complaint about flat girl being an alkeni. He originally was complaining about how alkeni should have the top half of a human and bottom half of a spider, and 'simply being able to shoot out webs from her fingers' shouldn't make her an alkeni. But then understood that there are people that like and dislike demihumans, and being chased around by a half-spider monster (so you are still getting chased by the bottom half of a huge spider) would probably turn off some people. So he just decides to call her spider-girl instead for obvious reasons.
But no seriously, motion sickness?