[Uchi-Uchi Keyaki] One Shota One! ch.1 [MrBubbles]

Sent off by his adoring, impossibly curvy mother, young Kouji's search for missing sweets at his friend's house lands him pinned beneath Tsuki, the teasing older sister of the household, who steers their bickering toward a nervous question about sex. One flustered realization later — each secretly convinced the other is in love — her petite chest presses down on him as she takes his first time in a sweaty, girl-on-top ride that ends in a deep nakadashi finish and a quiet vow to marry her. But just as the afterglow settles, the snack run returns with a cheerful "we're home!", catching them red-handed and kicking off these stories of boys and their older sisters.