You get a better idea. Instead of Dominant Will, how about Helping Hand?

Your gut is telling you that unless you act now, this could be your first and last meeting with a pro hero. You can't simply reach out and grab her head; on the off chance that she even lets you, she'll definitely get suspicious if you hold it on and on. You've got no reason to suspect she knew your quirk, but...

Wait! Maybe that's it! You tell Tsu to hold on one second before getting back out there. That wound on her head is still bothering her, isn't it?

"Thanks for the concern, but I'll be okay. A little scrape like this won't slow down a pro, ribbit!"

You think she's putting on a tough act for your benefit as a civilian, and a part of you really wants to recommend she get herself to a doctor... Then again, you suppose she probably takes bigger bumps than that in the field all the time. She isn't staggering or anything... So, you move onto your main point. You ask Tsu to let you use your quirk, Helping Hand, before she goes out. It'll help with that wound of hers.

"You have a healing-type quirk, ribbit?"

Sort of... You tell her it's more like a pain or stress relief quirk than a healing quirk. It'll help her stay in the fight without worrying about her injury... But, after the fight, she really ought to see a doctor. Seriously.

"I hate to impose even more, but... If it'll help me fight, I can't refuse, ribbit. Will it take long?"

You tell her it'll only take a minute or two. All you need is a minute or two of touching her head.

"All right. Thanks again, Ren, ribbit. Please, hurry!"

Her urgency reminds you that you're obstructing a pro hero's rescue work, and you waste no time approaching her. As she watches you with her dark, funny eyes, you place one hand on her head.

This is it... How tempting it is to simply cash in on this once-in-a-lifetime opportunity, here and now! Your first impulse, although you're ashamed to admit it, is to try and do something to forcibly draw this out. You could implant a behavior so she could never leave your room, or one that made her think of you all the time... But the part of you that's still a decent person reminds you that'd seriously screw with her hero work, and the part of you that wants to save your own skin reminds you that if you make a big, obvious change to her behavior, it'll definitely be found out. Either you'll end up in jail, or you'll end up getting your butt kicked by Tsu herself. Another notion you have to squash immediately is the idea to just go ham and make the chance count, for most of the same reasons you just considered.

No, the first use of Dominant Will (well, the second) needs to be to convince her "Helping Hand" is a real thing. So, you first focus on making that a reality for Froppy: You feel good when I touch your head. You shut your eyes and focus, sure that, now that you really need it, this'll be the first time your quirk won't work.

Still... even if it doesn't, this is probably an experience you'll remember for the rest of your life. As a kid, you touched the heads of your female classmates as part of those childish pranks, but this is nothing like that. You and Tsu are both young adults, and yet, here you are, with a hand in her voluminous, dark green hair. You wondered if even her male friends at UA had managed something like this.

And how does she feel about it? You don't have to guess: your Dominant Will is working just as you intended, and she has a wide, beaming smile clear on her face. That worked pretty fast!

Now that you think about it, this is the first time you used your power to make someone happy... Which would be a nice and wholesome thing, if you weren't lying to her to bring it about and if you weren't planning to use your extra time to make this more interesting. While your hand was still there, it was time for the second most important Dominant Will command for Froppy: Having your head touched by me feels so good, you want to make it part of your routine.

Your hands dig slightly tighter into her hair in anticipation, because after this comes the important one, the third pillar of your genius plan. If you can control Tsu not to think about sudden changes in her behavior, considerations like "this is the most important thing to use my quirk on right now" will be no more. And that goal is within your reach. With just a little more-!

Ah! No!!

Suddenly, Tsu draws away from your touch. You definitely didn't get that last one in there. You aren't even sure you got the second pillar! If you didn't get that, would Tsu even show up another time? Shit! You ask Tsu if she really has to go already? Healing Hand could do a lot more if she could wait a sec...

"Thanks, Ren, but I'm already feeling a lot better, ribbit! I can't waste another second getting back out there. That's an amazing quirk, though. Even as a civilian, you could help a little of people with that quirk, ribbit... Wait, didn't you call it Helping Hand?"

Dammit, that's right. You tell Tsu it was just a slip of the tongue.

"Oh? Is that a frog joke, ribbit?" She tilts her head at you curiously before turning her head and shooting her tongue out for the door as she planned earlier. Still, with her tongue around the doorknob, she waits for your response with her eyes locked on yours.

Crap, now you've even gone and offended her. You struggle for a response...

"A'hm jokehng," she tells you around her tongue, turning her straight face back towards the door as she flings the door to your apartment open. "Frog jokes are okay, ribbit. See you around, Ren!"

Tsu leaps cleanly from your apartment to the railing of the balcony. Low enough to clear the header, but high enough to reach the top of the railing, then deftly grab it with both her hands and her feet... Pro heroes are no joke. Suddenly, you remember she's going back into a fight. You shout for Tsu to remember she's still bleeding! Even if she's feeling better, she needs to see a doctor right after the battle!

You see her give you a simple nod, and then she's leaping from the balcony and out of sight. That battle's still raging in the distance. She's back in her world, and you're back in yours. But will she be back? She did say "see you around," but who knows if that was a general goodbye or if your "second pillar" has been successfully implanted by your quirk? It's impossible to say. You'd planned to go out, but, uh... There was a giant garbage monster still being fought pretty close by. Instead, you decide to join all of the gawkers watching the heroes fighting it.

This morning, you'd assembled a dream team of pro hero girls in your imagination, but those were all just that: dreams, fantasies. Now that you had actually met one, had a conversation with her, and even touched her, what was the point in thinking about the others? Just yesterday, you'd planned to never use your quirk again... Now, your mind is buzzing, trying to decide what you'd use it for first, if you had a chance.

Changing her behavior in a dramatic way that affected her hero work might be off limits... But, as though that limitation absolves you of all guilt otherwise, your mind rapidly fires off the things you might do if you had the chance to alter her private behavior. Her hands on your body... Your hands on body... The things she might wear, and the things she might not...

Is any of that actually okay? Didn't you change yourself in order to stop yourself from using your quirk? But that hadn't been for any selfless, moralistic reason: you'd just been thinking of keeping yourself out of trouble. If it's all in private, just between the two of you, what could be the harm? Really, it's all for the sake of stabilizing you so you don't snap in some other way. These are healthy fantasies... In a way, it's just another way Tsu would be protecting the people as a hero.

Just because you're having probably **** sexual fantasies about the heroine who's fighting to save your neighborhood while having sustained a head injury, that didn't make you a bad person! Not necessarily, with everything considered!