Have you taken a look at ryslig? It's a medium-paced-ish horror game (with a speed flux around the first few days of events) that works under the premise that characters are slowly turning into monsters. It's community based, and from what I've seen, is very backtag friendly. There are no castmates for Dorian, or for Cullen (yet; but I imagine there will soon be an influx given another app round). For Akihiko, there's a Persona cast that includes a Minato, Mitsuru, Ryoji, and Shinjiro.