The Seven Colored Alien from Hell's Onsen, Porori

Lala is seen watching a commercial on tv about the Tsumata Misami Hot Springs. She then tells Rito that she wants her own hot spring. Rito finds Lala attempting to build something in their yard. Lala then asks Rito to go get her a drink, so Rito heads to the store where he is suddenly attacked by Yami-chan as a test. Rito tells her that Lala is back at home building something, in which after hearing this, Yami-chan leaves. When Rito returns, he finds that Lala constructed a large drill machine which she intends to use to dig underground and hopefully find a hot spring. Mio, Risa, Mikado-sensei, Yami-chan, Haruna-chan, and Saruyama are all invited to join Rito and Lala dig underground. As they travel, they find Tokugawa's hidden treasure and the entrance to Atlantis, which Lala blatantly passes by due to there being no presence of a hot spring nearby. They eventually come across what is called the Seven Colored Hot Springs due to the water appearing as seven different colors. All the girls enjoy using the big and spacious springs, while Saruyama and Rito are stuck using a very small and cramped one. Saruyama decides to get out of the small spring and mess with the girls in the other hot springs. Rito soon follows, and sees Saruyama chasing after Risa and Mio, which Rito then tells him to stop. They come across Mikado-sensei and Yami-chan, who then punches them both with her hair stating that she hates ecchi people. Lala then tells Haruna she needs to leave the spring to try and find a hot spring she can bring back to Rito's house. Rito then finds Haruna and they try to start a conversation with each other, which is then interrupted by Lala who tells them that they need to leave quickly because she accidentally hit an underground volcano. They come across a civilization of moles who seek to rule the Earth's surface, but the moles are then killed by the flowing magma, and everyone returns safely to the surface.