My Dad is Too Strong - Chapter 39

Mary was an only child. She came from an ordinary family and worked at a publishing house. She worked diligently every day but was always harassed by her manager.

Transmigrated into the world of High School DxD, Roy believed he had been handed a life of luxury and glory. Born into the prestigious Lucifuge family, with his Sister Grayfia as his strict yet devoted older sister, he thought he was destined for greatness. 99,997… 99,998… 99,999… 100,000!!But... reality proved harsher: Roy lacked demonic talent and, despite years of training, remained a Low-Class Devil. his peers effortlessly achieve High-Class status, he’s been trapped in a cycle of endless sword practice and ridicule. Yet, he refused to accept mediocrity. Ten thousand sword swings a day, relentless training.. Until one day..[Ding! The Strongest Demon King System has been activated. Access functions to learn more.]---- High School DxD - Main World!1 - High School of the Dead [●] - First2 - Demon Slayer [●] - Second3 - Akame Ga Kill [●] - Third4 - Bladedance of Elementalers [●] - Fourth5 - Campione [●] - Fifth

This is a story about the protagonist getting the system, going crazy in the biochemical apocalypse, producing aircraft and tanks, destroying zombies, saving good people and killing bad people.

- Description from novelbuddy

Everyone says he is an iceberg, but only Maya Spencer knows he is a volcano, and moreover, a volcano that is passionately unlimited for her, an indulgently pampering volcano.