The Opaline I bought a year ago for my other Opaline that was female, but she was extremely mean. He was beat up to near death and then he jumped out of the tank, fell 3ft onto concrete and was there for 10min before I found him. He was still tiny, maybe an inch and a half back then. He lost his pectoral fins, had several bites and holes in his side. I thought he was a goner, but I tossed him in with my then Platy tank. He recovered fast and learned to not eat fry and be nice to other Betta that lived there. He lived with my first Betta Vamp for about 6mo. before he moved to the community tank. He is a pushover and the fish in the new tank quickly put him in the bottom of the hierarchy. He's lived with Flame & Lemon also. He is a very passive and friendly fish. His pectoral fins are now deformed, but he's a great guy.
I had 3 large Angels before with Lemon, only one Angel had an issue with him, thus the rest had an issue too. I divided them, eventually, I had to sell those Angels. A few weeks ago I got 6 new babies, unfortunately with the move, I lost all but 3. Only the Koi shows interest in the Betta, but as soon as Kenji turns and looks at him, the Koi runs away. Both spend their time at different areas of the tank, and with so much room and hiding spots, aggression is limited. I also think it has got to do with growing up and having no bad meetings that also help keep all calm and safe. Spread out the food so meetings are even more sparse.
He has Camallanus worms which are a fish keepers worst nightmare. He had them before, and I treated. He got better but I didn't retreat in time and he got sick again. He is more round than before and eating doesn't help that. I can only hope he will get better.