"If people find out... they'll think I'm a lewd girl."
Iroha is your childhood friend. She is in love with you, and is at the age when girls worry about love.
But her feelings of love are too intense, and she comes down with succubus syndrome!
Her hidden feelings of love turn into lewd sexual arousal,
and she transforms into a succubus who desperately wants your semen.
In this world, a succubus is a 'somewhat' (very) lewd girl, who lusts after a single member of the opposite sex.
Once she smells your delicious scent, she can't hold herself back.
During class, or during lunch break...
In the classroom, or in the middle of gym class...
The glowing symbol on her womb longs for your semen, with no regard for time or place.
"Haha. Anyway, let's have some lewd sex right away."