User blog comment:Chichiryuushintei/High School DxD BorN Episode 5 Review/@comment-3965848-20150502153708/@comment-24910433-20150502170236

Assuming Loki actually does control Issei, this could set up Vali in JD vs Issei. After all, now that Fenrir is taken care of, Vali has no one to use JD on. That could be why it shows them fighting in the OP, along with having Chichigami save him from Loki's control at the end or something.