Isawa Fosuta vs. Kakita Yosuga

My opponent has an activated Fosuta [already used his maho open and is remaining bowed] in his home. I targeted his Fosuta with Yosuga's iaijutsu limited. My opponent chose not to dishonor his Fosuta. He gives me the 1 honor and the choice to have 1 of Fosuta's ability not to be used until my next turn begins.

I chose Fosuta's maho open.

What happens now? a. Fosuta won't be atleast to be able to give out curse tokens but remains bowed? or b. Fosuta straighthens during my opponent's next turn or whenever with cards that can straighten him (Paid Off, etc.) ending his "now" unusable ability?

Just needed some clarification especially since Fosuta's ability to remain bowed isn't part of his trait but his ability. Thanks~!

•••• Relevant Text

Kakita Yosuga Crane Clan • Samurai • Duelist • Artisan • Master of Ceremonies Iaijutsu Limited: Target another player's Personality. His controller may dishonor him. If he is now honorable, gain 1 Honor and choose one of his abilities; it may not be used until your next turn begins.

Isawa Fosuta Spider Clan • Shadowlands • Shugenja • Inquisitor • Experienced • Unique • Onyx Champion After Fosuta enters play, Lose 8 Honor. Maho Open: Bow Fosuta: Lose 6 Honor. While Fosuta remains bowed, you may negate his straightening and, at the start of each turn, you may target a Personality and give him a -1F/-1C Curse token. After the next time this game Fosuta straightens or leaves play, destroy all Curse tokens.

What happens now?

Not much. If your opponent chooses to straighten his Fosuta during his Straighten Phase, which seems unlikely, then he will not be allowed to use Fosuta's Maho ability until your next turn begins.

Regardless of Yosuga's action's effects, Fosuta's controller can still negate Fosuta's straightening and give a Curse token at the start of his turn while Fosuta remains bowed.

Indeed, to prevent an ability from being used does not negate any of the effects of a previous action taken from this ability.

Abilities and actions: "The term “ability” refers to the static text on a card or other game entity, while an “action” is a process that starts at a particular point in time."