This was a very daunting task, especially near the end, but overall I'm confident in this prediction.
Title: THE THEATRE SUICIDE SCENE 5
Younger Girl: I was thinking you would never let me out to fight.
Shunsui: You know what to do, Nanao?
Shunsui: Well then...we must head back out, before he discovers us.
As they prepare to move out, Shunsui puts his head down.
Shunsui: I'm sorry...Kanawa...
100 years ago, Shunsui saunters through the streets of Seiretei. His eyes perk up when he sees someone up in front of him.
Shunsui: Ooh, Kanawa-chan! Need some help carrying those bags?
However, Shunsui's flight is cut short as a bag swings into his chest, knocking the wind out of him and sending him dizzily spinning about.
Kanawa: You mind your own business, Kyoraku!
We see Kanawa Ise, a woman who looks similar to present-day Nanao, but is bigger and wears her hair in a bun. Next to her stands a young Nanao, carrying a book in her hands.
Nanao: That guy's my division captain, mother! He's weird, but nice...
Kanawa: You haven't seen anything yet, dear. <To Shunsui> Am I the only person you can talk to now that Lisa's gone?
Shunsui: Kanawa-chan, I'd never consider you just a second choice!
Kanawa: Come on Nanao, let's go.
Kanawa drags Nanao by the hand and briskly walks away. Shunsui does not follow.
Several hours later, Shunsui sits inside his quarters drinking tea. Suddenly, the door opens, and Nanao comes in.
Shunsui: Well, this is unexpected. Care for some tea, Nanao dear?
Nanao: I want to know...why doesn't my mom like you?
Shunsui: Ah, yes...sit down, Nanao dear. You see...I've courted and flirted with a lot of women in my lifetime. But your mom...she was special.
Nanao: But she doesn't like you.
Shunsui: I know...and I can't blame her, she's a strong woman and I'm...me. But I stand by the principle to never give up on her until I die.
Nanao: You know...you're kind of stupid.
Shunsui feigns shocked outrage.
Shunsui: I wouldn't mock a man's dream, Nanao dear! Else you may eat your words!
Right then, Kanawa comes in, looking angry.
Kanawa: Nanao! Why did you go here without my permission!
Nanao: I'm sorry...
Shunsui: Please don't blame her...
Kanawa: We're going now!
Nanao: Oh, Captain Kyoraku! I forgot to tell you, but I achieved Shikai!
Shunsui: Really? That's amazing!
However, Kanawa's face becomes grim and she puts her head down. She then leads Nanao out the door.
Shunsui: Something didn't seem right with Kanawa...
Several days later, Shunsui is jolted awake by a large ruckus. Racing out of his quarters, he rushes to the training hall. There stands Nanao with her sword out. Almost everything in the room is broken, and Nanao has blood running down her forehead.
Shunsui: What happened, Nanao? Are there intruders?
Nanao: N-no! It's-
Right then, Kanawa comes rushing in.
Kanawa: Nanao! What did I say about you training alone?
Nanao: I-I'm sorry! I just wanna master my power!
Kanawa: Nanao...you know that's too much for you to do alone. Go back to our quarters, and I'll be back with you soon.
As Nanao leaves, Kanawa turns toward Shunsui.
Kanawa: Have you been asking Nanao to perform Shikai during training?
Shunsui: Yes...but she's never done it for some reason. She went on the verge of tears, so I stopped. What's wrong with her Shikai?
Kanawa: Only Nanao and I have seen it...and it is too much for a child to handle.
Shunsui: Then should I help her master it?
Kanawa: I appreciate your resolve...but Nanao does not like swordfighting at all. I will help her do what needs to be done.
Each day afterwards, Kanawa and Nanao head out into an abandoned clearing. Unbeknownst to them, Shunsui is watching from the forest.
Nanao: Mother...I don't want to wield this sword anymore!
Kanawa: I know, my dear. But until you gain full control of it, it's too dangerous! After you control it, you'll never have to wield a sword if you don't want to.
Shunsui: So I could never win your love, Kanawa...because someone's already won it.
Some time later, Shunsui is jolted awake as he hears a scream, as well as another sensation.
Shunsui: Kanawa...her spiritual pressure!
Shunsui races out into the clearing. Nanao is passed out on the ground, and Kanawa is lying with a great hole in her chest.
Kanawa: I'm sorry Shunsui...I failed in my task.
Shunsui: I'll take you...to Captain Unohana...
Kanawa: No...it's too late. But before I go...would you do something for me?
Kanawa: Please...take Nanao's Zanpakuto...and adopt it as your own.
Shunsui is astonished when he hears this.
Shunsui: B-but that's impossible! No Shinigami can wield and win over another living Shinigami's Zanpakuto...
Kanawa: It is possible...I read about a way. Please, Shunsui...she's not the kind of person who can wield this kind of power!
Shunsui: Very well...what do I do?
Kanawa: I'll tell you...but be warned...this process exists, but no one has completed it...they have all been killed.