Tsuihou Sareta Tensei Juukishi wa Game Sashiki de Musou Suru

The day a child turns fifteen, they undergo the Ritual of Divine Blessing. Already descended from a line of master swordsman, Elymas was supposed to succeed his father. However, he pulls the defective class, the Heavy Knight, and not only loses his status as future head of the household, but he's also exiled. With their unbalanced stats and seemingly useless skills, Heavy Knights are spoked of as a class for cowards and the lazy. However, Elymas knows the truth. The world he lives in is the same as the one of the game he used to play... It is the Heavy Knight that is the most powerful class of them all. Using memories from his past life, Elymas has set out to effectively conquer this entire world.

(Source: K Manga)