Kugo is the mc in my story Descendants and successor

He have two others friends which they got their power by keys inside a box at abandoned house 

Daichi and Maya is twin who are his friends, also have a little sister name Sarah

But one day, Sarah was killed mysteriously, but there's a track which is same as Daichi but it's all just misunderstanding and Kugo won't hear even a thing, his mind is corrupted
He also have another mode, and that is Ender mode when he got hit fatally 