Nagaharu Hibihana 
Mixed Bathing in Another Dimension: Volume 7 [EPUB ebook] 

After finally confronting the demon lord and coming to a peaceful resolution, Touya Houjou dives right into another problem. This time, the hero Cosmos has been kidnapped! Touya chases down the kidnapper, only to discover it’s another summoned hero, Ritsu Nakahana. Ritsu seems to have brainwashed Cosmos with her mysterious gift, and she’s even managed to enlist the prince of Jupiter into her ranks. The only way to stop her from taking over Jupiter is to…return her to Japan?! It’s the grand finale of our hero’s grand mixed bathing adventure!