I'm looking for a manga in which the main character (MC) reincarnates expecting magic or power ups, and finds himself weak and powerless. He has to train in a garrison like a commoner soldier and he's only good at running.
The first monster appears as goblins attacking the village, with the goblins seemingly being unstoppable killing machines. The main character hides in fear after seeing villagers and soldiers getting totally dismembered by them. The goblins are only stopped by the commander of the soldiers who has some kind of lightning speed strike skill.
The MC is kinda dark, slim, and depressing. He was a high school athlete who injured his leg, and when he stopped being an athlete everybody gave up on him, family and friends. He drowned in sorrow, and got interested in video games, occult mangas, and isekais. Now I don't know if I'm mixing stories, but I remember he waited until his 30th birthday, at which point he expected to reincarnate in another world. At first it seems he did not, but he ended up reincarnating in a medieval village inside wooden walls as a younger version of himself, still powerless.