Mad Party of Indigo Blue - S1.E4

Karen Ayanokouji, Jun'ichi's classmate, invites him and his class to her casual "home" party. He is at first not interested, but is dragged along by Minato who also receives an invitation. When they arrive Jun'ichi, Yuuhi, and company find that the party is actually a formal event on a huge cruise ship. Seeing how underdressed everyone is Karen loans them some formal wear, and Minato makes quite the impression on Jun'ichi when he sees her with her revealing dress. This causes Jun'ichi to have awkward feelings about his sister and asks her to cover up. Later, on their way back from the ladies room, the girls discover the kitchen is seriously behind schedule as most of the cooks are seasick. This prompts Minato and the girls to swing into action to save the party. The girls finish the feast and Minato puts on a show slicing up a tuna. Karen, feeling upstaged by the tuna show, puts on her own performance fighting against a giant octopus. This sends a scared Yuuhi running out onto the deck where she trips and activates the fireworks, which ricochet throughout the ship causing a fire in the party hall. Everyone escapes safely except for Minato and Yuuhi, and so Jun'ichi goes into the fire to save them.