Spring has finally arrived in Moomin Valley, giving way to another great adventure for Moomintroll and the rest of its inhabitants. With Snufkin coming home from his winter migration, the locals of the valley finally begin to rise from their hibernation. Finding a mysterious hat, the Moomins cannot bring themselves to throw it away due to its fine quality, instead hoping to eventually find its owner. While playing games with his friends, Moomin tries to hide in the silk hat. When his friends come looking for him, they are shocked to discover that Moomin has transformed into a hideous creature. Examining himself in the mirror, he is disgusted to find himself completely unrecognizable. Transforming back to normal after scaring his friends and family, Moomin and Snufkin decide to toss the hat in the river. As it drifts away, they begin to wonder who the hat belonged to and whether its owner will return for their lost possession.

Home to countless street acts and performances, Veludo Way attracts those interested in watching professional actors. After receiving a mysterious letter, Izumi Tachibana arrives at the venue where her father directed a once-popular theater group, Mankai Company, but learns that the building is about to be repurposed due to excessive debt. At the last minute, she convinces the debt collector to give the ensemble one more chance. He is willing to accept but on three conditions: their debut show must be successfully produced by the following month, the four all-male sub-troupes must be reinstated, and the debt must be paid off within a year. To top it off, Izumi herself must become the director. With no time to lose, Izumi quickly gathers five people for the Spring Troupe: Sakuya Sakuma, an enthusiastic high school student; Masumi Usui, a boy infatuated with Izumi; Tsuzuru Minagi, an aspiring playwright; Itaru Chigasaki, a mature office worker; and Citron, a friendly foreigner. Though they have little or no experience in acting, it's up to Izumi to train and prepare them for a performance that will restore Mankai Company to its former glory.

Edo-period Japan stands strong and proud, decades after its imminent doom was prophesied. The new shogun, Yoshimune Nobu Tokugawa, encounters an array of traditions that, to her modern judgment, make little sense. An epidemic exclusively rages among men, resulting in men making up only one-fifth of the population. Still, three thousand young, agile, and beautiful men serve in the Oooku—the shogun's Inner Chambers. To unearth the origins of the existing hierarchy where women head their families and govern the nation, Nobu reviews the chronicles of the odd disease. Customs and traditions have changed to accommodate for the plague; these new laws dictate the current culture and reflect the cruel story of the first female shogun, Iemitsu Tokugawa. Most notably, these customs seem to lead back to the moment a young monk, Arikoto Madenokoji, must abandon his way of life and devote his remaining days to the shogun and her Oooku.

Following their performance at the Black or White event, the idol group IDOLiSH7 is at the height of its popularity, with offers for various concerts and work coming in every day, much to the joy of the seven boys and their manager. However, as their fame continues to rise, Riku Nanase's health begins worsening due to the heavy workload. With the gigantic idol duo Re:vale showing interest in the group and the reopening event of the Zero Arena coming up, IDOLiSH7: Second Beat follows IDOLiSH7 as they not only struggle to adapt to the challenges of the idol life but also to face their personal troubles, all while continuously meeting the expectations of their treasured fans.