Is this against T.O.S?
" Quickly read the description of a persona that belongs to a forum account and make a posts in that forum. There are 100 personas. You’ll be given the account login credentials."
T.o.S. is intentionally the most difficult interface to get through. Unfortunately, it’s understandable.
Is there something against ToS here?
I don’t entirely understand your wording, but it sounds like you are offering to create 100 fake forum accounts for use in posting comments.
It might violate the ToS if a third party (the forum) doesn’t allow fake or multiple accounts. This forum doesn’t allow multiples. The only other thing I see is the word credentials which can be a trigger word.