...in the end, just what is this thing?

Enemy? Ally?

Well, isn't it like Sazanami's this thing

Or Oboro-chan's crab

Or this thing at the Card Display?

Seems harmless to me though.

She starts to get curious on "that thing" which she had completely forgotten.

Jump strength

Yellowish

Antenna?

Monoecious?

Bookworm?

Clever comment

Similar to a slug