The 18-year-old cousin of Professor Gojo Shiouji (the creator of the Ropponmatsu units), and serves both as his intern and lab assistant. Absent minded, easily flustered, and accident prone Umi is nevertheless very kind hearted, and hardworking; although her personality combined with her general clumsiness amounts to a great deal of trouble for the Professor, and his work. Umi is an avid cosplayer, being shown in a multitude of different parody-esque outfits throughout the course of the series, which regularly proves to be a source of irritation to her crush and employer Shiouji. Umi's first appearance is Volume 12 of the manga, but does not become a prominent character until volume 15, when she becomes the caretaker of the amnesiatic Excel (given the name Teriha Shiouji.)
Umi Rengaya only appears in the manga.