When regular salaryman Yoshida wakes up one Sunday morning after a long night at the bar, the last thing he expects to see is that his tiny apartment has a new resident—an unfamiliar high school girl. The previous night, despite finally gathering the courage to confess to his boss and longtime crush, Airi Gotou, Yoshida was rejected. After drowning his sorrows at a bar with his good friend Hashimoto, Yoshida headed back to his home in a drunken stupor, only to run into Sayu Ogiwara, a runaway high schooler. She asked him to let her stay the night, and with his judgment clouded by alcohol, Yoshida complied. Now, with his head on straight but with no memory of last night's events, Yoshida has Sayu explain just how she ended up sleeping at his apartment. Having listened to her story, Yoshida finds himself unable to kick her out—especially after learning that she came all the way from Hokkaido! So, despite his reservations about sheltering an underage girl, Yoshida allows her to stay, and their life together begins.

Yuuta Hoshitani enrolls in the prestigious Ayanagi Academy in hopes of finding the high school student who inspired him. The academy is well-known for producing exceptional musical talent, but students must first compete for acceptance into the Musical Department. At the top of the department is the Kao Council—a group of third-year students who possess a great deal of influence over the school and admission into the department. The fastest route to entering the department for Hoshitani is to find a way into a Star Team, which would allow him to be taught by a member of the Kao Council. After catching the eyes of Itsuki Ootori, Hoshitani finds himself under the tutelage of the Kao Council's most eccentric member. Alongside him on Team Ootori is his roommate, Tooru Nayuki, fledgling Kabuki actor Kakeru Tengenji, the quiet Shuu Kuga, and Kaito Tsukigami, the younger brother of famous Ayanagi alumni Haruto. As Hoshitani struggles with his lack of talent, his teammates must also overcome their shortcomings. Facing opposition from other talented Star Teams, including the other four members of the Kao Council, Team Ootori must carve their own path as they aim to perform in the Ayanagi Festival.

High school student Issei Hyoudou is your run-of-the-mill pervert who does nothing productive with his life, peeping on women and dreaming of having his own harem one day. Things seem to be looking up for Issei when a beautiful girl asks him out on a date, although she turns out to be a fallen angel who brutally kills him! However, he gets a second chance at life when beautiful senior student Rias Gremory, who is a top-class devil, revives him as her servant, recruiting Issei into the ranks of the school's Occult Research club. Slowly adjusting to his new life, Issei must train and fight in order to survive in the violent world of angels and devils. Each new adventure leads to many hilarious (and risqué) moments with his new comrades, all the while keeping his new life a secret from his friends and family in High School DxD!

Yokosuka Girls' Marine High School is bustling as they welcome other all-girls maritime high schools for interschool competitive games. Full of excitement, students from different years gather and interact with one another as the festivals and tournaments commence. In the meantime, mixed feelings fill Akeno Misaki—captain of the distinguished Harekaze class—and her executive officer Mashiro Munetani when their instructor informs them of an opportunity for Mashiro to lead the Hiei class. As a result, Mashiro needs to make the difficult decision soon, and Akeno needs to confront the state of the situation. The pair face another challenge after Yokosuka finds itself in another pinch. A group of pirates has captured a water purification plant and sea fortress, threatening the safety of the sea. Akeno and Mashiro now must command the Harekaze class in the midst of a dire predicament—all while dealing with their own difficulties.