XING JIA HUN JIANG ZHUAN

Song Yunxiang, humanity's final mecha-sorceror, was reborn back to his schoolboy days with a powerful System. Last time when he was young, he was shunned for his lack of spiritual constitution. Because he was weak, he could only watch as his friends and comrades died in the oncoming war. In this life, he returns with a System along with 60 years of combat experience and technical knowledge. This time, back on campus, he will use his newfound power to create new mecha and destroy the monsters… All his regrets, all the friends that he missed, this time he will not make the same mistakes. (Source: Tencent, translated) — Description from AniList community (anilist.co).