That's what it looks like from my reading of the threads...

Okay. Here are the three possibilities I propose:

A) Ryoji runs into Minato before Jin and idk. They talk or something. If fighting happens, Ryoji is apt to merely defend himself and not attack back, particularly as it's just going to sadden / upset him to really see what's happened to this Minato. Er - as far as his mind / personas / the fragment of death inside him go as well as seeing someone he regards as a friend because being AU doesn't matter to Ryoji so unhappy and mentally suffering... So if Minato did lash out at him, Ryoji would just let him hoping maybe it'd help or something.

B) The above-mentioned encounter occurs, they go their separate ways, and then perhaps sensing how active Thanatos is later in killing / beating on people, maybe Ryoji comes looking again and joins in the go after Jin and Minato brigade.

C) He just comes upon things when it's boss fight time and joins in, because death is cheap in the tower, and if it's the only way to stop people from being in more pain / causing more pain, welp.

... or I guess D) wait for another time to meet~