Mizu ni sumu hana

It happened in a blink of an eye. Rikka Nikaid is a normal school girl whose life is thrown into chaos when her bus flips into a lake while on a school field trip. She is the sole survivor. Once she is released from the hospital, she tries to regain a regular life and even starts up swimming again. However, a black haired woman attempts to attack Rikka repeatedly while in the water. She is Rikka Mizuchi, a girl who has lived for centuries with the help of a golden seed that her lover Izumi gave her every forty nine years. This year, Izumi gave Rikka N. the seed, and Rikka M. is determined to kill the other Rikka before the girl is fully assimilated with water. Yuzuru, Rikka N.'s weak, university student cousin she's loved since childhood, learns about the other Rikka. But it turns out that Yuruzu may not be so human after all. A long, long time ago, there was a white dragon and a black dragon. They fought to see who would rule which part of the sky. And the white dragon fell, and the black dragon assumed he was dead, and soon forgot about him. But the white dragon had gone down to the humans, and became one of them. A story told to the first born sons of the Nikaid family, who have dragon blood running through their veins. One day, with the help of a female relative who would be named Rikka, the white dragon would be revived. As it turns out, the black dragon is Izumi and the white dragon's reincarnation is Yuzuru. However, he kept his feelings for Rikka a secret, because the way to revive the white dragon is through sex, where the white dragon would devour the girl's life. He tells her the way to revive the white dragon after rejecting her when they were about to have sex, Rikka already realizing that sex was how to revive him. But as Izumi causes climate disasters, trying to force the white dragon to do something about it and fight him, Yuzuru refuses to devour Rikka in order to fight back. Rikka M. learns that she also has Nikaid blood coursing through her, and offers herself to Yuruzu. Rikka N. stops her. As floods happen and the rain is boiling hot, Yuruzu asks if Rikka would give herself to him and she agrees. He devours her, and the white dragon is revived. After going to the lake where the seed came from and freezing her, the white dragon and the black dragon finally have their rematch, the one Izumi wanted so desperately. When Rikka M. realizes that the white dragon and the black dragon have equal power, she offers herself to be devoured by Y