What if the twins were from Steven Universe.
1. They are normal humans that are friends with the gems. They have their own gem technology and weapons. They understand alot of things about gems and can even rival Mario in knowledge.
2. The twins are 1/4 gem. They can't use any gem powers unless in a dire situations, like barely conscious and going to die if they do nothing. Their gems are fragments of their parent. Their parent is still alive because they have the majority of the gem still in/on them.
The twins gems are completely in their bodies and when they were fused with the lacma, their gems also fused with it.
Their demons didn't become one with them, luckily. Even without being a half gem, they can only fused with their demons.
Now if the twins were ever fully died and was resurrected they will become half gem. Their lacama infused gem with come to the surface of their bodies. Now with training they can use gem powers and magic. They can fuse with anything now.
Just imagine Ritchie and Michael fusing because then they'd have a god and demon in their bodies/minds.
You can choose if their gem is a diamond or something different.
-June 28,2020-
