What if you are reborn as a demon after a funeral?

He was reincarnated and became a demon with extraordinary talent and a long lifespan.
Although he was born an orphan with living parents and had to fend for himself, and had to be careful of both his own kind and humans, it didn't matter. At least he suddenly got a system when he was three years old, but the system was unexpectedly not very useful.
However, he was still transported back to the past, where he befriended Frilian and became the junior brother of the ancestor of human magic. But he soon discovered that his friend had a great deal of prejudice against demons.
It's alright. Fortunately, my childhood friend and cousin, Awula, has made something of herself. It's just that... I used to boss her around a lot when we were kids, so our relationship is a little complicated.
It's not a big problem. He even met the strongest hero, but... the other party died a little too early.
As he oscillated between humans and demons, he gradually realized that he couldn't seem to rely on either side.
"There's no other way, I'll have to rely on myself."
He set himself a new life goal—to defeat the current Demon King! To become the new Demon King—tentative.