Alexander Snow- a sixteen year old boy. He participated in an assassin program for 13 years, until the facility was destroyed. He was the only survivor and escaped to Europe. Three years later he was hunted down and killed. He then found himself in heaven, where he was reincarnated before he could get any real answers.

But after being reborn, he was immediately abandoned by his mother and left alone in the cold forest, where he was found by a woman, who took him with her. From that moment on, he started his second life as an assassin again in a clan full of them.

[Cover not mine. I found it on google.]