MTL - The Rise of Otaku - Chapter 583 aquarium

In his last life, he was a superstar that dominated the entertainment circle. In this life, he is a rebellious second generation wastrel.

Lassen, a young man who has failed at everything in his life, has had enough. Disillusioned with the world, he decides to end it all. But instead of dying, he wakes up in a parallel world, armed with a strange system that can accomplish anything he desires. Trapped in his room, reading novels and savoring every page, he has no intention of participating in the fast-paced world outside.Yet, despite his desire for peace, the world changes every time he makes an appearance. Everyone treats him like a genius, a being capable of disrupting the very fabric of reality, without lifting a finger. A powerful system, a new life, and a world that adapts to him: why complicate things when you can have everything without effort?The Genius System tells the story of a man who, although having everything to change the world, prefers to watch it evolve from the comfort of his room, through the pages of his books.

In Ten Heavens Domain, full of respected powerhouses, juvenile Ling Tian accidentally obtained a mysterious iron sword. He refined the Supreme Martial Dao, studied the Divine Spirit Array Laws, fought Ten Thousand proud and arrogant Heavenly Clans, and was undefeated! Seven Feet Sword Tip sweeps away the world, within the Ten Heavens, I am the Supreme God Monarch!

- Description from Novelupdates

Failing in his job hunting, Sanada Kyouichirou was hopeless in this society. When kyouichirou had thrown himself towards the bottom of a cliff. When he woke up his body had returned towards when he was in fifth grade of elementary school. He did not want to have any regrets in this life so he had decided on building up an harem in this second life.

The elder sister that he admired, a senior and president of the student council at a school for rich young girls, a strong minded upper classman at school. The poison fang of Kyouichirou who had pretended to be a innocent child attacks those girls.