DXD Mixed bloodlines
I don't own DXD or any of its characters
The two heavenly dragons fought again and again but eventually their as is known by almost the entire supernatural world their physical bodies were destroyed and their souls were sealed in two separate gears to continue their feud through their wielders by the biblical God.
However, a fact the is known to few even fewer than those privy to the fact that the biblical god was dead was the fact that in total each of the heavenly had one spawn each before they were sealed, a daughter of dividing and as son of boosting, these children would be raised in secrecy and were taught to contain their power to avoid a repeat of the fathers' dispute carrying over to the next generation and avoid the risk of them being hunted but the factions.
Many years passed and eventually the two met and as dragons do when they find an opponent of equal strength they challenged them for their territory these fight ended in a stall mate again and again and eventually an attraction grew between the two and they settled down in what used to be a dragon nesting ground otherwise known as kuoh which was now devil territory but the two settled and within a couple of weeks they were expecting a child.
5 years later
Issei ran from his friend Irina a girl whom he met through his parents and currently they were playing tag much to Irina's despair as she could never seem to tag her friend no matter how close she got but she never gave up and that was something Issei admired and true to his playful nature he often restrained himself so that he didn't out right harm her when they played.
But the two kids had fun and were relatively at peace with their lives as they were but the world as it stood seemed to think this was an act worth punishing as the dragons were discovered by a very specific group of fallen angels or rather the fallen's second in command and those under his command.
The group was currently watching the children with intent of killing the human and kidnapping the hatchling but just as they group began to move Issei's parents arrived but the barrier had finally enclosed itself before it could be canceled and thus realizing that they were no doubt caught the fallen began to attack.
Issei's mom quickly gathered the two children up and moved them away but as she did so she heard her mate roar in pain and she turned in time to see a weapon pierce her mate's head killing him quickly Issei's mom let out a scared whisper "Dragon slayers!" and broke a part of the barrier shoved the two children into the break as she told them to run to Irina's home before she turned to face the fallen transforming as she did so.
test story
feel free to make your own takes on this if you want