Magika no Kenshi to Shoukan Maou - 5.6 — Surprise Attack Operation-Magic War・Okehazama

The story is about a boy entering high school, who answers a strange call from a public phone one night. The caller challenges him to a bet: She’ll remove the birthmark which he sees as the cause of so many problems, and he’ll have fifty days to win the heart of a girl he’d considered far beyond his reach. And with this, a very strange summer begins.

(Completed) She and he were born on the same year, month, day, and time, and on their first day of life, their unscrupulous parents arranged their future marriage.From then on... she began to cling to him.As a child, Luo Mengmeng would say in her baby voice to Gu Zhihan, “Husband, I want to marry you,” but he would grimace and respond, “Who would marry you!”When they grew up, Gu Zhihan hooked her chin, pinned her against the corner, and smirked, “Mengmeng, I heard getting married is cheap nowadays, I'll treat you.”From birth to kindergarten, elementary, middle school, high school, and university, they had always been together.[Growth literature, from childhood to adulthood, exclusively adored]

This is a story about a legend, of one that can never be forgotten.
Summer, first time down the mountains in 16 years, after being raised by his 3 masters and Fairy sister.

‘Why won’t you follow the Rules of society?’ The rules are the tool made by the strong, so I follow my own rules.

‘Why won’t you just use your brain instead of your brawn?’ Idiot! Have you ever seen anyone use their brain, to get back at an ant that bites them!? No, they just casually step on it.

‘Oh, everyone says you’re a first-class beauty huh?’ well, I’m sorry but even you are not qualified to be my wife. Only a ‘Summer class beauty’ is worthy enough!

‘My enemy is sick?’ Oh, don’t worry, even if you’re on your last breath and I feel it’s beneath me to slap shot you dead. I’ll just fix you up and then beat you!

‘Who am I?’

“I am Summer in the spring, the autumn, and the winter, I’m the world’s first above the heavens!”

Follow me, Summer Day as I step by step become known as the world’s first master, the world’s first doctor, the world’s richest man…… a lot of other world’s number one, but most importantly, The worlds happiest man.

- Description from Novelupdates