this is kinda trash but I'll give chapter two a try
1) parents that LOVe him throw him away for having no magic no thanks
2) his master never told him about having no mana this whole time? No bro
3) demon lord suddenly appeared after 50 years? If it hadn't been defeated in the first place why wait 50 years, bruh
4) how did the MC not realize about having no mana? Where's his brain?