Rentarou's Family was selected to win a ticket for reservations to the pre-opening of the brand new Serious Onsen created by the Serious Group, headed by a distant relative of Iku's. As the group arrives and start making use of the onsen, it becomes clear just how seriously the Serious Group lives up to its name.
It starts when the girls gets swallowed up and dispersed throughout the place by the rapidly expanding suds of the onsen's body soap due to the shower's water pressure being too strong to use to rinse it away. Kusuri gets trapped in a jet bath, forcing Iku to block the water so she can escape. Shizuka gets stuck in a Jacuzzi blasting water up in the air, and Nano becomes crippled with fear when she tries to rescue her, though their combined weight enables them to escape.
Hakari finds Karane in a breast enhancement bath, but the latter refuses to leave until Hakari enters the bath as well. Mimimi and Meme get stuck under a waterfall shower, but the latter manages to make herself disappear from under the former by asking for a kiss on the neck, allowing Meme to pull Mimimi out from under the water. Hahari finds Mei in a cold bath and wades through the water to help her warm up.
Eventually, Rentarou and all the girls are able to regroup, and the group of 17 decide to try and relax in the paradise bath. This proves so relaxing that it leads to everyone Giving Up the Ghost.
Tropes:
- Chekhov's Gun: After explaining her Escape Artist abilities in Chapter 46, Meme manages to put her disappearing act to use in such a manner in this chapter.
- Giving Up the Ghost: Happens to everyone at the end of the chapter while in the Serious Paradise Bath.
- Hot Springs Episode: Rentarou and the girls are invited to try out the Serious Onsen in this chapter.
- Serious Business: All of the Serious Group's products have names that start with "Serious".
