I hope I’m not the only one who noticed this here. All these so-called “possessions” we’re seeing in Burst are actually just the afflicted Bladers being driven by a strong emotion and/or desire for something.
Shu wanted to become stronger not just because he wanted to defeat Lui and Free, but because he wanted to fix his broken promise to Valt.
Aiger’s dark resonance originated from his fear of Phi destroying Achilles after seeing the latter do the same thing to Vise Leopard.
Delta is being pressured by Diabolos to seek out strong opponents so it can prey upon the Beys’ lights. It’s also likely that Diabolos is feeding off of Delta’s jealousy of Dante’s closeness to Valt.
You've got a point there. I actually do think he's the only exception and really was possessed. I was just stating some theories after delving more into the possible reasons why (it's also mentioned that he allowed Spryzen to control him).
Also, did you notice that during Delta and Pot's battle, it was the classic Angel vs. Devil situation?