Issui
Part of the Yuriban pantheon, Issui is the goddess who governs water and inevitability. She is particularily strongly associated with moving water of all sorts. Issui's philosophy focuses on the inevitable change that encompasses every life. Despite how it may seem on the surface, her teachings focus more on how time and good things slowly wear away the pain of the past, allowing one to continue to move forward towards their future.
Issui is an emotional deity, despite her patience, who is portrayed as feeling things deeply and with as much power as a rushing river.
Associations
Issui's colors are, unsuprisingly, shades of blue. Most typically, one finds blue-green as the primary color used in artwork and items associated with her. Any aquatic animal is considered to be at least loosely connected her.
It is believed that the Yuriba River is one of her sacred areas and there are a number of myths about her manifesting among its waters. Furthermore, the location of the Yuanquannyanniichuan (Naiad-girl) spring is a sacred place to her; it is possible that the Shuitanyanniichuan spring might be as well. In general, all water spirits and avatars are considered to be blessed by her. (It is possible, although unproven, that she favors Allya in particular.)
In mythology, Issui is the lover of Harumeku and Fuyuzora; the three goddesses are a longstanding triad in mythology. She is, however, also on good terms with Amanohara as the two goddesses work together to produce Yuriba's inevitable precipitation.
Issui is also rumored to be the cause of the green flash that sometimes appears off the Boardwalk on Maboroshi.