【Marine】My overprotective and naughty sister

Story
The protagonist is the youngest and eldest son, born and raised in a family with four sisters and one brother.
When the boy is finally born, his sisters love him very much, and even when he grows up, they don’t want to see him die.
This overprotective attitude did not go away, but escalated.

The eldest daughter was a school nurse, the second daughter was a gym teacher, and the third and fourth girls were seniors.
All of them go to the same school as the main character and live with their brother at home and at school.
Then, the results of the main character’s physical examination at the school come in.

This is a story about a young girl who is in love with her brother, but she is not sure what to do about it.

“I think the reason my brother is not growing well is because he is not getting enough nutrition… but I take care of his daily diet, so what should I do?

“Breast milk is necessary to provide the baby with plenty of nutrition. Shouldn’t we start giving it to her now?

The only people who can protect the main character in this family with no parents are the sisters! I’m sure you’ll agree.
In order to give the protagonist breast milk, they obtain a mysterious secret potion called “Bonne Demacour"!

And from that day on, the days of being breastfed by your sister begins!