Samezoku e no sasagemono

The following content is intended for mature audiences and may contain sexual themes, gore, violence and/or strong language. Discretion is advised.

“I’m prepared to be this man’s wife…”
The Tangata Clan chief's son, Avel, is frustrated with the Miyaru clan who lives on the other side of the island. “Each year, one adult will be offered to the Miyarus from the Tangatas.” Their ancestors from long ago created this law in order to avoid conflict with the strong Miyaru clan, which is said to have the blood of sharks in their veins.
One day, when Avel is attacked by a beast, he is saved by Tukiri from the Miyaru clan. Avel’s wariness is lessened by how unexpectedly friendly and kind Tukiri is, but the moment Tukiri realizes that Avel is bleeding, his looks suddenly change! His appearance suddenly changes into something inhuman, and starts to go into heat.
Avel is flustered by this Tukiri. Yes, the Tangatas are a tribe of people with peculiar bodies where “the first time you have sex determines your gender role.” If one plays a female role the first time they have sex, their body will become that of a female…!
“You can’t… I’m next in line to be chief…!”
While resisting, Avel is once again swallowed up in a whirlpool of pleasure??