Ishiyama High is a school populated entirely by delinquents, where nonstop violence and lawlessness are the norm. However, there is one universally acknowledged rule—don't cross first year student Tatsumi Oga, Ishiyama's most vicious fighter. One day, Oga is by a riverbed when he encounters a man floating down the river. After being retrieved by Oga, the man splits down the middle to reveal a baby, which crawls onto Oga's back and immediately forms an attachment to him. Though he doesn't know it yet, this baby is named Kaiser de Emperana Beelzebub IV, or Baby Beel for short—the son of the Demon Lord! As if finding the future Lord of the Underworld isn't enough, Oga is also confronted by Hildegard, Beel's demon maid. Together they attempt to raise Baby Beel—although surrounded by juvenile delinquents and demonic powers, the two of them may be in for more of a challenge than they can imagine.

Demon King Ahriman has a problem: his daughter, Doux, loves everyone! Consequently, Ahriman had to halt his invasion of the world in the worry that his daughter's behavior is not one befitting someone of her kind. She loves making friends, helping others, and bringing happiness to all creatures including their enemies, the humans. Ahriman, however, congratulates Doux for her good deeds instead of scolding her. With the help of his aide Jahi, who is assigned as Doux's master, the two try to get rid of her kindhearted nature—so that the Demon King's daughter goes from a cute, adorable, and nice little girl to an inhuman, cruel, and twisted little demon.

Despite occasional setbacks, Operation Strix has remained on track to extract sensitive information from the enigmatic politician Donovan Desmond. To this end, spy Loid Forger has managed to maintain his pretend family consisting of his telepathic daughter, Anya; assassin wife, Yor; and their clairvoyant dog, Bond. Still the only one aware of everyone's true identities, Anya tries to sustain the family's cohesion while working to befriend Donovan's son Damian, her Eden Academy classmate. However, Anya's efforts instead earn her another Tonitrus Bolt, bringing her closer to getting expelled and jeopardizing the operation's success. Hearing the news, Loid faints from shock. In his unconsciousness, he reminisces about his tragic past and his journey to becoming a spy. Realizing what Operation Strix means to him and the world, Loid finds renewed motivation. Although they each work toward their own covert goals, the Forgers continue to cherish their chaotic yet blissful family life.

The contrastingly cute dragon, Al, the first king-killer in the demon world, who has a full combat score but is ready to die and longs for a happy retirement, bumps into the cunning human magician Le Fei, and accidentally becomes a super dad who raises Le Fei's son Dino. Will Dino be an ordinary and happy child, or will he bravely pick up the Warrior's Holy Sword and face his own destiny... (Source: Bilibili, translated)