Toilet-bound Hanako-kun -The Musical- is a stage adaptation of the Manga Jibaku Shounen Hanako-kun.

[HELIOS] After the 13th class entrance ceremony, the newly appointed rookie "Heroes," Junior and Faith, are assigned to the West Sector. However, the team they're assigned to is unusual, with only one mentor, as per the wishes of Mentor Leader Brad. Furthermore, Mentor Keith has no desire to teach, and leaves the two rookies to their own devices. Frustrated by the lackluster team atmosphere, Junior asks to be transferred, while Faith remains apathetic. Far from improving teamwork, the rift only widens. Meanwhile, an incident caused by [Eclipse] sets the gears in motion that connect the past and the present. It all began four years ago, at [Lost Zero]. --The death of a certain "Hero."

New Million, "the city where a million dreams come true," has developed thanks to the efforts of its Heroes. In this city, visited by people from all over the world, a dome-shaped stadium floating on the sea has been born. It's called "Grand Sea New Million." Plans to hold a summer festival as the opening event have been floated, and the stadium management has asked the Heroes for their help. [HELIOS] has agreed to fully cooperate for the sake of the city. Not only will the Heroes perform at the festival, but they'll also be helping with the event itself, working across sector boundaries to prepare for the festival's opening. However, one problem after another arises... Furthermore, behind the scenes, [Eclipse] and his allies are secretly plotting. Will the "Summer Festival" be able to open safely?

Four years have passed since the "Lost Zero" incident. Keith Max still believes in the survival of Dino Albani, who was presumed dead, and continues to pursue him. Meanwhile, Brad Beams keeps a close eye on Keith's precarious actions, striving to find answers to his own doubts. At this time, a new "Eclipse" threat creeps into the city. In the midst of this chaotic situation, standing before the "Heroes" is "Zero," with whom they have fought countless times. As they confront each other once again, the lost time begins to move violently once more.