Ugetsudou Antique

At a mysterious antique shop that appears only on rainy days, Sou finds the keepsake of his grandfather that he supposedly lost a long time ago. He asks the owner, Tsukiji, who has a different air about him, to hand it over to him, but it's not money that this shop accepts as payment. With a fearless smile, the condition that Tsukiji put forth is "Please give birth to my child"!?
(Source: Tokyomangasha, translated)
Note: Includes one extra chapter.