Heya Beans!
How old is the Betta? Often in the rising hormonal awakening after 6 months to about 1+ year of age anything goes. Each is of course his own personality. After the age of being young and sassy, strong and territorial, they can start to mellow.
Sometimes they just go towards things but don't really kill anything. I'd make sure it had places to rest in the plants near the top of the tank if you get any bottom additions like a few dwarf cories say. And have soemwhere for them to hide. BUT I have seen a Betta turn sideways to the substrate and hunt baby fish (changed tanks and there were a few baby Guppies I didn't see) or shrimp into cracks and crevices.
Just be prepared to not put anything very costly or your other favorite fish in with him as one morning it might be shredded up /or laying dead in the bottom of the tank.
More than once a Betta keeper has had all love and cuddles for months and often to the yearish point, only to find a mayhem event of destruction, obliteration and death...