I understand. But I looked at Discord and signing up there requires an e-mail address. As I want to stay fully anonymous, that is a no-go for me. Also it turns out that the solution provided by @spiz0r provides no accurate time stamp, which you need.

Would it be possible to use PGP? This can be achieved by exchanging public keys (once) and then posting encrypted answers using your public key signed with mine. Public keys can be freely posted without anyone else being able to decrypt (for that you need the receiver's private key).

A clear advantage this way would be that the answer is in one central place (as a reply on your Steamit post) but a disadvantage is that it takes some doing in order to read it (copy/paste into PGP software).