[9] - I was the Second Son — I Brought a Game Relic and Became a Knight-Mage Overnight

Reincarnation, a second son’s grind, and a strange relic that refuses to be ordinary. Follow a young trainee’s harsh days at a rural castle as he trains under heavy armor, hides the knowledge of another life, and discovers a mystic object that changes everything.

Short summary:
He wakes in the body of a twelve-year-old knight’s son, forced to train while the estate favors the eldest. Breath training and heavy-armour drills are how ranks form — but the protagonist’s past-life experience and a mysterious cube in a battered crate give him tools no normal knight ever sees. Expect medieval castles, country markets, knightly etiquette, and the slow turn from second son to something far more dangerous.