Okay but to be OVER 10 TIMES BIGGER than another man in any context is INSANE. The world record for longest penis is 18.9 inches. Assuming our protagonist has a WORLD RECORD BREAKING 19 INCH PENIS - which would be less like a penis and more like a MEAT ROD OF INTERNAL HEMORRHAGING (Your average HORSE is 14-18 inches long.) That would mean that the blacksmith's penis is LESS THAN 1.9 INCHES LONG. And not just smaller - SIGNIFICANTLY SMALLER as the samurai girl noticed a SIGNIFICANT CHANGE IN LENGTH. Assuming the blacksmith was even just AN INCH SMALLER (debatable whether a woman would notice a difference of an inch outside of incredibly specific contexts) that would make the blacksmith 0.9 INCHES LONG WHEN FULLY ERECT. The vaginal hole lies 0.5-2.5 inches past the very front of the labial folds (although take that with a grain of salt as I'm not sure if my source is reliable on that one) So for any vagina even approximating AVERAGE that's not even going IN. Were the new spots she felt the hero reaching PENETRATION? Maybe that's why the hero's wife always shot down any of his sexual advances BECAUSE SHE DIDN'T WANT TO BE FUCKING SPLIT IN HALF. Also, I'm pretty sure if a woman who was comfortably accommodating 2 inches of person suddenly had close to 20 INCHES OF PERSON INSIDE OF HER SHE'D ACTUALLY FUCKING DIE.
Although I'm just being a shitter because I think due to the square cube law volume increases and decreases exponentially compared to surface area (I think, I never learned this shit in high school), so a penis that's shrunk to a 10th of its normal size wouldn't necessarily be a 10th of its normal length - especially depending on what his length to girth ratio is.