So... I just got myself an idea after going like reading a fanfic about DD and To Love Ru. Although the idea that came to my mind was completely different.
So you guys probably know about "guardians of the galaxy” right? So you guys know that star lord was technically kidnapped right. So basically it's similar. He said it's kidnapped. I don't know if he should be like a little kid or where Raynare kill him. He got kidnap was being turned into an experiment by that Organization that had Yami although I have no idea what the organization was called. But anyways he was turned into a super soldier they tried desperately to break him to make him evil but Issei stayed strong. Also, he met characters like My Favorite Tearju
Eventually, he escaped... And trained XD time for some Goku training! So yeah, he got extremely strong he eventually became an Assassin and fought Gid in his full power and Issei using his skills, Boosted Gear, and his Balance Breaker destroying planets. But eventually Issei lost to Gid. So Issei join Gid and is known as the Second Strongest in the Universe. Also Issei meet Gid family and got along with Sephie despite Issei noise bleeding the nature to keep things, professional and his Daughter let's say they got along.Evenly the war happened and Gid became king of the universe.
Issei was sent to a mission sadly never returned his ship accidentally malfunction and crash into earth but he escaped by using his Gundam and landed near a ocean and is back at Kouh and found a Leviathan princess and became her bodyguard.
Meanwhile, the universe has been going crazy ever since the second strongest has been lost so Gid an irresponsible person push his paperwork to the side to find his buddy.