Mikuni is a jellyfish merman and a friend of Wakasa in the anime Orenchi no Furo Jijō. He occasionally visits the home of Tatsumi, a high school student, where Wakasa has taken up residence in the bathtub. Mikuni's body is composed of ninety-nine percent water, which allows him to easily shrink or grow in size. He can also split himself into many smaller versions and possesses the ability to deliver electric shocks, often forgetting that touching others will sting them.

Mikuni requires no food and sustains himself solely on water, making him very low-maintenance compared to Wakasa and other aquatic visitors. This quality appeals to Tatsumi, who appreciates Mikuni's frugality. Despite needing water to survive, Mikuni has a strong wanderlust and frequently wanders on land. His personality is gentle, laid-back, and easygoing; he rarely becomes flustered and exudes a peaceful, shy demeanor. However, there is a hint of a more enigmatic side to him, as Wakasa and Takasu suggest that Tatsumi does not yet understand what Mikuni is truly like.

In the story, Mikuni serves as a supporting character who adds a serene presence to the group of friends. He does not drive the plot but contributes to the comedic and slice-of-life interactions in Tatsumi's home. His key relationships include his long-standing friendship with Wakasa and Takasu, and his cordial but understated connection with Tatsumi, who finds him endearing and economical. Mikuni shows little personal development over the course of the series, remaining a consistently calm and mysterious figure. His notable abilities are his size manipulation, fission, and electrical stings, all of which are tied to his jellyfish nature.