This is a quite frequent kind of situation when people have a history of booking travel online for their SO prior to marriage and/or seeing the name changes showing up on the government-issued photo ID -- more so when there is autonomy in the relationship whereby the SO handles their own name change matters largely independent of the spouse/partner following up on the matter.

Japanese immigration authorities on arrival are highly unlikely to care about such situations.

The airline reps are a more realistic issue, but most won't even try to make a show stopper of it.

The TSA is many things but they are highly unlikely to be a show stopper for such situations.

Personally, I would just travel as is, taking what Onobond mentions, and not worry about it. That said, my risk tolerance level and ability to adjust to situations on the fly isn't the same as everyone else's.