Game Chishiki de Saikyou ni Natta Mob Heishi wa, Shin no Jitsuryoku wo Kakushitai

A nameless gate guard secretly possesses the greatest strength among soldiers. In his past life, he was deeply familiar with the game world into which he is now reborn as a low-level mob soldier. Using his knowledge, he becomes extremely powerful but conceals his abilities to avoid changing the game's events. One incident, however, draws attention: he effortlessly defeats a formidable demon that even the hero finds difficult to fight. He happens to do this in front of his favorite heroine, leading to whispers about his strength spreading. As his reputation grows, he must navigate the consequences of his hidden power while staying true to the game's original path.