Honestly my memory is so bad, I just remember the mc being a strategist for the army or something? he also showed how to create bombs and the ml had a high rank, maybe he was an emperor , there was a bit where mc fought in the frontlines in disguise? and ml recognised him, it wasn't world hopping I think because he mostly stayed in this one world. there was another character who liked some chic and hated the mc but grew to have a crush on him.
Thank you so much!! it was in my reading list and I knew I nearly finished it but couldn’t identify which one!! that’s correct! I was always wondering about it for a while. Greatly appreciated