a female Red Devil may work as a companion.... if he allows.
That reminds me of a neighbor who had a RD for years and saw my Tilapia buttikoferi and how aggressive it was in my tank. Against my advice, he purchased a tilapia assuming that another aggressive fish would be able to co-exist with his RD. But the Tilapia was too small so he had to put a divider up, "Until the Tilapia is large enough to defend itself". All the while the RD was constantly trying to knock the divider down to get to the poor tilapia.
A few months later...
In one corner a 12" RD, in the other a 10" Tilapia. He removed the divider, re-arranged the decor and went to bed. In the morning he called me and asked if I wanted another Tilpia for my tank. I asked why, was the RD beating up on the fish? He answered a sad no. The Tilapia killed the RD.
Moral of the story? None. I just admired my Tilapia the more.
, will they eat mine, because I'm sitting on bowl full right now
...