[Sakimori Dan] Sanae Challenge!! (COMIC Mugen Tensei 2018-05)

A dutiful salaryman's painfully ordinary life hides one deliciously not-normal secret: coming home to Sanae, his adorable niece blessed with a comically impossible bust that bounces with every excited greeting. What begins as 'baby-making practice' under his reassuring hand quickly spirals into sweaty, breathless sessions where the little girl discovers just how twitchy her body can get, tearfully begging her beloved ojisan to keep moving even as she melts under his touch. Between bath-time 'washing' lessons and hand-holding strolls through the city, Sanae dreams aloud of the day they'll become papa and mama—and her uncle happily resolves to raise his innocent little girl into a proper mom.