This is not bad; so far I give it 7.5/10, rounded up.
I feel like it skips over the protagonist's actual abilities in favour of social interaction, which is not ideal; knowing his limits is the basics for making him seem clever by circumventing those limits.
I also feel like he ought to have impressed the Yakuza girl in several more ways before she decided to marry him.
(Revealing the extent of his subspace skill might be jaw-dropping, for example.)
And spacing out events more to let the main pair grow up a bit would have been good.
But at least it's fairly novel.
Though it feels a bit like an adaptation where the artist is omitting things that happened in the book, to get out of drawing complicated stuff...
What we need now IMO is more focus on the MC's family, friends and activities outside the yakuza.
Gotta have some contrasting normal people, to accentuate the weirdness.
And the author needs to show off their smarts a bit. Impress me with some plot.