I think it's the older brother of the classmate. We aren't to the point in the timeline where the classmate is the hero yet.
Oh we aren’t I thought we were
Because as far as I remember when the spider got outside the classmate became the new hero
the anime is following the light novel, and as far as I can tell it's jumping around the timeline like crazy. It is a bit hard to follow which is why i prefer the manga because it doesn't jump between now and 15 years(?) into the future i believe.
Wait she said hero
Does that mean he’s the spiders old classmate
Because in the anime the (new) hero’s her old classmate