In This Life, The Greatest Star In The Universe - Chapter 280:

Three Days of Happiness is a novel by Sugaru Miaki, also known as Fafoo. It’s a rewritten version of the story originally posted to 2ch.

The premise of the story revolves around a shop where one can sell away the remaining years of their life, and the consequences of doing so.

“I Say A Little Prayer” is a short related story which was posted along with the novel’s release. It spoils some things about the main story, but nothing major.

15 years ago the world discovered magic as well as mythical beings (basically beings from various legends) in another dimension. Humankind learned to summon these dangerous mythical beings and use their power to great effect. Seven countries formed contracts with these “mythical beings” and gained their allegiance as a result. The mythical beings will choose their summoners on their 14th birthday and give them a stigma. Schools have been set up to train summoners and magical swordsman (basically bodyguards that give the summoners time to cast their spell) as a result.

15 years later after the finding of magic Kazuki Hayashizaki is chosen as a summoner and given a stigma to indicate that. This is surprising since males aren’t chosen as summoners due to their low amount of mana compared to females. As the first male to be a summoner Kazuki is under a lot of scrutiny by almost everyone.

To complicate matters his sister (who’s a magical swordsman) is against him going into summoner school to train there as a summoner. Because summoners and magical swordsman have a cat mouse thing going on where summoners look down on magical swordsman as inferior so his sister naturally is against him going there. She’ll stop him even if it means going to war.

Kazuki however is determined to thrive in summoner school and has already determined to give it his all. Even if he’s the lowest ranked student (ranked E) and his fellow students intend to demean him he’ll prove himself as the strongest summoner.

Chen Che traveled through the strange world of immortality with an overload plug-in.

Every time he enters the overload state, his body will experience some discomfort.

The training speed of the exercises has been improved, and the weak cough.

The speed of boxing comprehension increased, and the arm was red and swollen.

The speed of supernatural power cultivation has increased, and the headache is splitting.

…

Chen Che, who was suffering from an external illness, chose to practice in a low-key manner.

It was not until the first year of Daozong that the new emperor ascended the throne and began to rectify the dynastic order, killing traitors…

Then something unexpected happened!

What?

The father I never met turned out to be a big traitor?

It also affects me to be exterminated by the nine clans?

never mind! Stop pretending!

I see who can kill me!

- Description from novelbuddy