https://wccftech.com/devil-may-cry-5-online-co-op-mod-available-now-on-pc/

Devil May Cry 5 had a very limited online co-op feature, as you might recall. Through the so-called Cameo System, other players could randomly appear in your game, sometimes joining in battle as well.

Needless to say, this system didn't serve much of a purpose in practice. Now, however, modders Dante and Raz0r have published a Devil May Cry 5 Co-Op Trainer mod on Nexus, vastly increasing the online co-op capabilities of the game.