In the Guest House With Mana-san

Please ravish me until I get pregnant...

For the sake of his father who suddenly collapsed due to illness, Subaru Kanameishi (19), who was attending a cram school in Tokyo, gives up on his college entrance exams.

After over ten years, Subaru is recalled to the Kanameishi main family house, located in a region deep in the mountains. For the purpose of continuing the Kanameishi bloodline, the main family demands that he begin babymaking with his older female cousin Mana (36), who he had previously thought was his aunt.

In order to pay for his father's treatment, while still finding his bearings Subaru goes along with the demand being made of him...

(Source: DLsite)

[Note: This has 2 near-identical versions, one is a hardcore version with bar censors and the other is a softcore version marked "DM" with full censorship. The covers are slightly different but the story is the same.]