asuya

Roy died during a war against the Evil God Cult, but somehow, he returned back in time to 30 years in the past where he was just a boy who awaken his summoning magic. 
Just a few days before his death, he became the only Aura user in a world of magic. 
Using his knowledge and experience, he will become an Aura user again, faster than his previous life. 
Accompanied with a shape-shifting black slime, he will make sure to protect everyone he cares about and win against the Evil God Cult.

The Only Aura User In Magic World

The next day, I brought Albert and the others to the Monsters Kingdom to introduce the mermaids.

"So they are the mermaids. It's good that you gained an extra force underwater. Especially since Spot and his children are busy training," Albert said.

"Yeah. Though their fighting skill is only around the level of the angels when I first brought them here. And they are poisonous as well. Normal healing magic doesn't work if their poison is mixed in your blood or you somehow swallow it. But if it's on the skin, you can use healing magic. Well, there are still many things to experiment. So I'm going to bring some prisoners here for experiment," I said.

"…You really don't care at all about human lives," Albert said.

Submarine