I looked up Japanese measurements units. Using imperial units would be ridiculous. They have ''Shaku'', 1 Shaku being equal to 30.30 cm/11.93 inches and the subdivision "Sun" or "Cun". Going by that scale of measurement, the dick would be roughly 20cm/8 inches, which is not too far fetched.
This artist draws good, but they seriously trigger salty emotions since they're constantly deleting their art post on Twitter at random intervals. Are they scared of getting their Touhou art reported?