Shin High School DxD - Volume 1 afterword

Based on the popular Vocaloid series, by HoneyWorks, called “Kokuhoku Yokou Renshuu (Confession Rehearsal)“:

Natsuki, a third-year at Sakuragaoka High School, who holds unrequited feelings for her childhood friend, Yuu, who’s in the Film Club. However, instead of being honest about her feelings, she makes him be her confession “rehearsal” partner. Unable to say her true feelings, things start to get complicated when Miou and Akari, who are also in the Art Club, get involved! Will she ever be able to confess for real!?

The Adrasia empire on the Vogel continent. There is a battle over the throne of such an empire that possesses powerful military and vast territory.With the successor undecided, the children of the emperor are vying to expand their power. However, there was one prince that everyone says will definitely not become the emperor.The seventh prince, Arnold Lakes Adler. The young man who was inferior to his younger twin brother in every way, the dull prince.Incompetent and lethargic, Arnold wastes everyday just playing around. However, behind the scenes, he is one of the only five SS-Class adventurers called ‘Silver’.Seeing the intensifying battle for the throne he decided “I don’t want to die so let’s have my little brother become the emperor…”This is the tale of absurd secret manoeuvres of the prince who is uninterested in the title of the emperor.

Lin Yun, 36 years old, a widower, a mid-level manager in a private enterprise, is a single father, who has recently felt that he is encountering a mid-life crisis. Professionally, he faced adversity; domestically, he was in a cold war with his 14-year-old daughter; physically, he suffered from periarthritis and spoke daily of his agony. In the past few days, he had also uncovered a secret — his daughter was being a “Magic” girl. With the body of a young maiden, she battled extraordinary monsters and protected the city from attacks — this is the common perception of a “Magic” girl. But he was very aware that being a “Magic” girl came with life-threatening dangers. Should he stop her, or respect his daughter’s choice and find other ways to protect her? Gazing at the Heart Flower in his wardrobe, now covered in dust, Lin Yun, the former “Magic” girl who retired 19 years ago, was facing the third major decision of his life.

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates