[Hoshino Fuuta] Niji no Kuni no Futago Tenshi (Koinu no Shippo to Osatou to) {Chin²}

Little angel twins Lily and her brother play among the storybook clouds of a rainbow kingdom until grasping tentacles erupt to strip them bare, leaving both children flushed, itchy, and aching with a strange heat they don't understand. Their flower-fairy tormentors flit away with a cheery command to mix together and make a healthy seed, abandoning the confused siblings to their own instincts. Alone above the clouds, the pair surrender to that ache, bodies locking together in a breathless first union that leaves warm seed spilled deep inside his sister.