Seinarukana Gaiden - Seirei Tenshou ~Kowareyuku Sekai no Shoujo-tachi~

The world of Kougyoku (crystal). A world that was told to hold the legendary medicine, "Inochi no Shizuku" (Life Drop). Many were those who tried searching for it, but nobody was able to find passage to the world.

Christopher Tangram, a treasure hunter for life. Wielding the 5th rank Eternity Sword, "Ryuushou" (dragon flight), he has been able to obtain a map with the world of Kougyoku's coordinates on it. Riding his trusty airship within the branches of Jikanju (Tree of chronicle), he flies toward his destination. But...

There are monsters dancing in the sky. There are people getting slaughtered with no place to escape. And the island of treasures is nowhere to be found. There are girls fighting against the innumerable abominations. Their elegant bodies a bad match for their graceless weapons, the girls lash out with their Eternity Swords. They who are born from this world of Kougyoku are the kin of Cryst.

Christopher, as an outsider, is mistaken as the Hero by the Cryst race, and asked to save the world before its ruination. He came looking for a treasure, but was drawn into a deadly war. All the while looking for the treasure, his battle to save the world of Kougyoku and the Cryst race begins here.

[Translated from Homepage]

Seirei Tenshou is a branching adventure game with 2D action-shooter elements. It's characters are the sub-characters inside crystals in Seinarukana.