Listless geek Mizuto Irido and introverted nerd Yume Ayai seemed like a match made in heaven, connected by their mutual love for literature. Unfortunately, their differences gradually grew, and they separated just after their middle school graduation. But, as if by divine comedy, the two find themselves reunited as step-siblings. A rivalry begins to brew between the former couple, both unwilling to acknowledge the other as the older sibling. In an attempt to "solve" this issue, Mizuto and Yume agree upon a rule: whoever crosses the boundaries of siblinghood norms loses, and the winner will not only be called the older sibling, but also get to make a request. However, now that they live under the same roof, the lingering memories they share start to influence their actions—possibly rekindling the feelings that may not have been fully extinguished in the first place.

The third season of Tate no Yuusha no Nariagari. After defeating the Spirit Tortoise, Naofumi has no time for rest. An attack from the next Guardian Beast is imminent, but the three other Cardinal Heroes have gone missing. So, Naofumi and his party set out to search for the legendary trio.

On Christmas Eve, four-year-old Miri Unasaka arrives in Tokyo completely alone, in search of her father. The bright lights and merry atmosphere guide Miri to a big hotel and a man with a delicious-looking cake. However, the child has just unknowingly walked into the center of an elaborate, foolproof plan for assassinating a dangerous mafia boss. Professional assassins Kazuki Kurusu and Rei Suwa live together, fleeing memories of their grim childhoods and avoiding emotional connections. When their mission goes awry and they end up bringing Miri home, there is only one reasonable thing to do: return Miri to her mother. But the girl's innocent laugh and pure worldview quickly enamor her to Kazuki, who secretly enjoys playing a parent, and it is not long before Rei's impenetrable heart makes room for Miri. Miri's every move is unpredictable, and Kazuki and Rei find raising an energetic child harder than any of their missions. Although it presents a great risk to their careers, Kazuki and Rei—both assuming the affectionate nickname "papa"—decide to provide Miri with a normal childhood despite all the odds stacked against them.

Unlike his friends, Takumi Fujiwara is not particularly interested in cars, with little to no knowledge about the world of car enthusiasts and street racers. The son of a tofu shop owner, he is tasked to deliver tofu every morning without fail, driving along the mountain of Akina. Thus, conversations regarding cars or driving in general would only remind Takumi of the tiring daily routine forced upon him. One night, the Akagi Red Suns, an infamous team of street racers, visit the town of Akina to challenge the local mountain pass. Led by their two aces, Ryousuke and Keisuke Takahashi, the Red Suns plan to conquer every racing course in Kanto, establishing themselves as the fastest crew in the region. However, much to their disbelief, one of their aces is overtaken by an old Toyota AE86 during a drive back home from Akina. After the incident, the Takahashi brothers are cautious of a mysterious driver geared with remarkable technique and experience in the local roads—the AE86 of Mount Akina. [Written by MAL Rewrite]