SISTERITUAL [COMPLETED]

At the Kusuzuki Shrine built to seal away the wicked one…
For generations, the masters of the shrine have served their duty to protect the people of the land.
However, this seal is not perfect.
Miasma pours out, ever so slightly.
And so with every generation, the masters of the shrine must carry this miasma in their bodies and eliminate it.
One day, the previous master of the shrine passed away. His son, Yahiro,
inherited his father’s role, but he was too young to partake in the inheritance ceremony…
Little by little, the miasma seeped into the earth, and the land began to decay.
Years passed until Yahiro was at last old enough to perform the inheritance ceremony and accept his role as master of the shrine.
The flood of miasma naturally gathered inside of Yahiro and started to eat away at him.
With no preparation, no knowledge, he still had no idea what the true role of the master was.
Several months later…
Yahiro is summoned by his grandmother, and finds out the truth.
About the seal. About the miasma that gathers inside him.
About the strange things that are happening to him.
And about the ceremony in order to prevent them…
“Now… This way… Master…”
The ceremony involves him… having sex with the shrine maidens.
He must unite bodies with his older sister, Maina, and his younger sister, Suzu.