Okami Wa Nemuranai - Chapter 35.7-8

Miguel transmigrated into the Wild Beast World in the body of a useless teen with the same name as himself after he was betrayed by his disciple, the Harem Emperor, for a knowledge and universal secret that he recently uncovered.In the Wild Beast World, humans could contract Wild Beasts through their Summoning Grimoire, a mysterious book that fated individuals can awaken at the age of 18.In this world of summons and beasts, Miguel awakened with the Beauty Sign-In System, which allowed him to contract legendary beauties as long as he signed in at a specific location.On his first sign-in, he received the Holy Daughter of the Red Family, the Fiery Empress of Legend.Using the Wild Beast World and the Sign-in System as a starting point, Miguel swore to return to the Immortal Cultivation World and settle scores with the Harem Emperor once and for all.Follow Miguel's journey as he reaches for the apex, becoming a legendary figure in all worlds.

One day, a villainess came to the orphanage.“I absolutely can’t stand children!”“How can someone my age have a child? It doesn’t make sense!”“What’s so great about these little creatures that tire you out all day long…”Setting aside her dislike for children…Somehow, after she arrived, the children started gaining weight.“It’s all because of the contract, you know?”That’s what she says.While personally feeding them sweets she made herself.

This is a world where humans, demons and mysterious beasts coexist.

Humans cultivate mysterious qi. Demons cultivate corporeal bodies. Mysterious beasts cultivate soul perception.

A legend says that in the middle of an endless rainforest, there are extremely powerful existences; they are called demon kings.

Some demon kings have a tyrannical corporeal body, some are experts in illusions.
Some demon kings are proficient in magic, some can even move mountains.
Some demon kings are able to sense things thousands of miles away.

These demon kings rarely appear in the human world. Even if they emerge in the human world, they would reincarnate in human form; assimilating with mankind while seeking to breakthrough realms…

- Description from Novelupdates

A 29 year old civil employment exam student wakes up in a blank white room and meets a baby angel. This baby angel informs him that he died in his sleep due to heart disease like his father and grandfather. Remembering his mom and their last conversation he says that he will take on a series of life and death tests that the baby angel offers him. From this point on he must put his life on the line and fight in the stage called ‘Arena’. And Every time he clears a test he will gain abilities and weapons to increase his strength. All to clear the tests and get his life back. This is his story of his fights in the ‘Arena’.