Third-year high school student Jirou Yakuin is in love with his childhood friend and classmate, Shiori Sakurazaka. Thus, he hopes to be paired with her for the "marriage practical": their school's practice of randomly selecting boy-girl pairs to live as pretend married couples while monitoring and rating them on how close they have gotten. Meanwhile, the lively Akari Watanabe wants to be assigned to her crush, the popular and good-looking Minami Tenjin. Much to their dismay, Jirou and Akari find out that not only have they been paired together, but so have Shiori and Minami! Determined to be with their crushes, Jirou and Akari strive to earn as many points as possible, as the top 10 pairs earn the right to switch their partners—so long as both couples agree.

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! [Written by MAL Rewrite]

Childhood friends Tomo Aizawa and Junichirou "Jun" Kubota do everything together, whether it be training or just enjoying a fun day out. Anyone would think that these two are best friends for life. The only issue is that the tomboyish Tomo is in love with Jun, but he regards her like a brother. At the start of their first year of high school, Tomo confesses her feelings to Jun. However, her rough mannerisms and lack of hesitance to throw a punch do nothing to sway Jun's heart. Realizing that he will remain indifferent to her affections unless she does something about it, Tomo must find a way to knock some sense into Jun and open his eyes to what is right in front of him.

Reeling from her recent breakup, Momo Ayase, a popular high schooler, shows kindness to her socially awkward schoolmate, Ken Takakura, by standing up to his bullies. Ken misunderstands her intentions, believing he has made a new friend who shares his obsession with aliens and UFOs. However, Momo's own eccentric occult beliefs lie in the supernatural realm; she thinks aliens do not exist. A rivalry quickly brews as each becomes determined to prove the other wrong. Despite their initial clash over their opposing beliefs, Momo and Ken form an unexpected but intimate friendship, a bond forged in a series of supernatural battles and bizarre encounters with urban legends and paranormal entities. As both develop unique superhuman abilities, they learn to supplement each other's weaknesses, leading them to wonder if their newfound partnership may be about more than just survival.