デカパイ♥ナマイキ♥妹魔王♥～デカチン♂ガチイキ討伐記～（Dekapai♥Namaiki♥Imouto Maou♥ ~Dekachin♂Gachi Iki Toubatsuki~）

You are a NEET who has failed the university entrance exam twice and is now living at home as a ronin student. Your father has already passed away, and you live with your mother and younger sister, Mao.
They have spent their days together peacefully, if not amicably.

However, Mao, who used to innocently follow you, has grown up to be a bitch who humiliates you whenever she sees you. And in the past few years, her breasts have also grown rapidly, irritating not only your mind but your cock as well.

One day, while your sister's attitude and big tits are getting on your nerves, your mother tells you about Mao, who has been nodding off at school for the past month or so and increasingly going out after school without telling her where she's going. She asks you to look out for her, but then decides to go away on a business trip.

You decide to live a short life together with Mao while paying attention to your mother's wishes. You are grateful to your mother for her kindness and encouragement, but you also feel a sense of shame. But she turns the tables on him and says, “I don't want to be ordered by my brother, who's a fucking ronin!”, this hurt him deeply.

Mao goes to sleep one night and only enough her body starts becoming transparent, She suddenly wakes up and immediately falls in love with her brother who is worried about her, but she soon regains her usual mood and begins to order him around. He is immediately put off by this and heads right to his room. When you leave your room, something is amiss.

You find that Mao is nowhere to be found in the house. You remember that her body became transparent, you immediately run out of the house frantically searching for her but she is nowhere to be found. You return home anxiously but you eventually fall asleep as if you had fainted.

When you wake up, what you see in front of you is the huge ass of a beautiful woman with big tits who calls herself a saint sucking you off. Being a perverted virgin you immediately begin eating her out and eventually end up having sex.

Turns out, you are a hero who has been summoned to another world. Your mission is to defeat the Demon Queen. The Demon Queen suddenly appeared and ruled over the demons with her mighty power.
She changed the world's official language to Japanese, eliminated studying, and orders cooks around the world to develop and serve her delicious sweets. She also turns all who defy her, human and non-human into cats.

Now is the time for a virgin's big dick, which had no use, to become a sex sword to defeat the demon Queen in a different world!

[From official site]