I don't mind that Chiaki was real, even though it resulted in her horrible, horrible death. Ultimately it's helping to make Izuru more interesting.
We barely knew anything about Izuru before DR3. He could have been a more interesting person without a real Chiaki.
Like, what happened to the anger he clearly had at the end of DR:AE? It hinted at a more complex relationship between him and Junko that didn't hold true here.