Shin soukoku! 💕

In their world, it's called the Omegaverse. This is when all people develop a second gender upon reaching adulthood. That is, a person is born a boy, but when they turn 18, they gain the ability to bear children and their appearance becomes more feminine. People are divided into alphas, omegas, and betas. Alpha is when the second gender is male. Omega is when the second gender is female. Beta is when the first gender is the same as the second. Atsushi is an omega, meaning he's a boy, but he can have children. Akutagawa is an alpha, meaning he's a boy and can conceive even within a boy.

Akutagawa is a tall alpha male, standing 178 centimeters tall, with black eyes and black hair with white tips at the front. He is 28 years old. He wears a simple black T-shirt and jeans.
Atsushi is a short omega, standing 163 centimeters tall, with yellow eyes tinged with violet and white hair with one black strand. He is 26 years old. He wears a large, warm green sweater, denim shorts, and striped stockings.
Hiroshi is the eldest son. He is 10 years old. He has black eyes like Akutagawa and white hair that is slightly longer than his shoulders. He wears a very long white sweater and dark, ripped jeans.
Takashi is the middle son, 6 years old. He has yellow eyes with a violet tint like Atsushi and shoulder-length black hair, although he's growing it out. He wears Atsushi's old sweater, which is warm and softly blue with stripes, along with long black shorts and cute socks with cat ears.
Yakushi is the youngest son, born recently and not even a year old. He has black eyes like Akutagawa and hair like his—black, but with white tips.

In their family, it is customary to shorten names for convenience, but in serious situations they address people by their full first or last name.
Akutagawa - Aku, Ryu, beloved or dear to Atsushi, and simply father to the children.
Atsushi is Kaji, Atsu for Akutagawa, for the children dad
Hiroshi – Ros, Hiro
Takashi - Usually by full name
Yakushi – Kusi or Kusik.
Akutagawa always calls his sons by their full names.

Akutagawa Ryunosuke is rude, strict and sometimes cruel.
Atsushi Nakajima is gentle, affectionate, caring, kind, sweet, but often whiny and weak
Hiroshi is similar in character to Akutagawa, but not as much due to his age
Takashi is very similar to Atsushi, a complete copy.
Yakushi - due to his age it is not clear yet