A/N: According to one (non-verified) source, December 12th is Zack's birthday. Unfortunately there's no way to confirm this short of actually asking him, but regardless: Happy Birthday, Zack!
"Angeal, what day is it?"
"It's the twelfth, Zack."
"Oh. Okay."
"Why?"
"Huh?"
"That's the fifth time you've asked. Why?"
"Uh... Nothing important, I guess."
"Which means there is something."
"No! I mean, yes. Or maybe."
"So something happens today, and you're trying to remind me of it. What is it?"
"Uh... Guess!"
"What?"
"Twenty questions, Angeal! Better start guessing, 'cause time's ticking!"
"It's called Twenty Questions, Zack, not Twenty Seconds."
"You're still wasting time."
"Okay, is it an historical event?"
"Uh..."
"And stop saying that."
"Ugh, fine. And I can't answer that. It's yes and no, sort of."
"Hm. Does it occur on this planet?"
"You think too big. Of course it does."
"Does it happen every year?"
"Sorta. But it's slightly different every time."
"What's that supposed to mean?"
"You'll find out if you keep asking."
"You do realize that missions are a bad time for games, right?"
"Ah, we'll be fine. Seventeen more questions, Angeal."
"Hm."
"Doesn't count."
"Is it a celebration?"
"Yup."
"Big?"
"Huge."
"All right, is it Christmas?"
"On the twelfth?! What holidays did you celebrate, Angeal?"
"Not many. We were poor."
"As you never cease reminding me."
"Zack, there was nothing -"
"Fourteen questions."
"Is food involved?"
"Tons."
"Then my chances of guessing this holiday are slim."
"Don't beat it in, Angeal. Just keep guessing."
"Is any large structure utilized in the festivities?"
"Uh...huh? What kind of... Never mind. I guess one could be..."
"Does the festival occur at night?"
"It can. In fact, it'd probably be even better that way. I need to remember that."
"Is there light and music?"
"Yeah. Maybe you did have some pretty cool holidays, after all."
"So it's a huge celebration, which sort of changes every year. There's food, a large building, and light and music after dark, right?"
"Uh...I guess."
"Is it celebrated everywhere?"
"It could be celebrated anywhere, but only so long as a particular something is there."
"Is there fire?"
"Sure. It sort of has something to do with the food."
"This is becoming too easy. Are animals involved?"
"No."
"That's a relief."
"Wait a second, do you already know? What do you think it is?"
"Let me keep guessing and you'll see."
"No, hold on. I wanna know. Is it violent?"
"Zack, I'm guessing, you're answering. You can't switch."
"Fine. And the answer's no, by the way."
"You realize you're answering your own -"
"Six questions left."
"Wait, that one counted?!"
"I answered it, didn't I?"
"You also asked it!"
"Tonberry at ten o'clock."
"Where?"
"Made you look. Keep guessing."
"Do some people not celebrate it?"
"Apparently you don't."
"I was -"
"Poor. Keep going."
"Does it cost a lot of money?"
"To celebrate? Dunno. I never had to finance one. So what's your final guess?"
"I have four guesses left."
"Yeah, but you'll want to save those in case your first guess is wrong."
"..."
"Well?"
"...It's a barn fire?"
"WHAT?!"
"Zack, the inevitable summer barn fire was the highlight of the year in my youth. Once the fire was put out, there was a celebration, with music and food for everyone... Zack?"
"That's twisted!"
"Maybe I ought to invite Sephiroth this year."
"Angeal, you wouldn't! Besides, that's not even the an-"
*Beep.*
"What was that, Angeal?"
"I texted Sephiroth."
"Wha...uh...you...oh, crap."
"What's wrong, Zack?"
"I need to go. I just remembered that...uh...is training over?"
"Fine. If you call this training."
Zack was out of the Training Room before the simulated Wutai had entirely dissolved. Angeal's PHS buzzed as Zack left, and he glanced down to read Sephiroth's reply to his invitation to Zack's birthday party. The general accepted, but also informed Angeal that Genesis had taken a mission to Banora on short notice and couldn't attend. Which was probably for the best, Angeal decided, because Genesis and Zack notoriously didn't get along well. But right now, he needed to finish getting everything together for the party. He chuckled to himself. He couldn't believe that he'd actually gotten Zack to think that a burned-down barn was cause for celebration in Banora. ...Where was Zack, anyway?
His PHS buzzed again in answer, and Angeal's eyes widened in horror at the message.
Took new mission to Banora. Departing immediately. Gotta go burn down Gen's barn before you and Seph get here. Wish me luck.
Angeal rammed the phone into his pocket and took off for the Director's office. If they didn't recall Zack fast, both him and the barn would be burning before long. Angeal hoped Genesis was on the farthest side of Banora possible.
A/N: I don't think Zack was actually going to Banora at all. I think he ran off and hid somewhere and sent Angeal the text just to panic him. And then Angeal hurriedly sends Gen a text saying, "guard your barn," and Genesis ends up failing his mission because he's so busy trying to figure out what the heck Angeal meant.