One inbox, read by the person who makes the games
0n1 is a one-person studio, so there's no ticket system and no call centre — mail lands with the developer. Player support questions are answered first; everything else as soon as possible.
There is an oni on the door, though. It can answer questions about the games straight out of this site's pages, and it'll show you which page it read. It isn't the developer and it can't do anything on your behalf — for that, the email below still goes to a person.