A/N: Never had a place to fit this into, but here's what the twins look like.
They both have the same brown hair and hazel eyes, and they're both the same height. Yoshi has chin-length hair that's a little bit longer on the right side while Yuki has his shoulder-length hair pulled up into a ponytail.
"I don't think this is a good idea..." Eleven-year-old Yuki told his twin sister as they peered around the corner at a group of yakuza.
"Quiet, Yuki!" Yoshi sharply whispered. "We have to show these guys who runs this town!"
"But I think they're the ones that run it!" He whined.
"Well, they're not!"
"I don't want to do this, Yoshi-nee!"
Without warning, Yoshi leaned forward and bit his ear.
"Ouch! W-why did you do that?" He asked, looking at her with tears in his big, hazel eyes.
"So you'll know who's the boss." She answered him, her eyes lingering on his pained expression before she placed a kiss on his ear. "There, it's all better."
Yuki sighed. "Alright, I'll do it... Since I have no choice." He looked like he was about to cry.
"I knew I could count on you, little sis!"
He really started crying. "You always call me that... Uwaaa..."
Yoshi pouted. "Just go out there and distract them, just like we rehearsed!"
With another sigh, Yuki stood up and dusted his skirt off. Despite being a boy, Yuki has a very lithe, feminine body; and everyone tells him that he's cuter than Yoshi, even Yoshi herself.
Yuki timidly walked up to the three yakuza who were standing around, glaring at the people walking along on the other side of the street. Their faces were hardened, each one looking like he was thinking about who he was going to kill next and what he was having for dinner afterwards.
"U-um... excuse me, sir..." Yuki spoke up, stopping in front of one of the men. His voice was very soft, and he didn't need to make any effort to sound like a girl.
Their eyes slowly turned his way, the men glaring down at him. Just as Yuki thought that he was done for, the yakuza in front of him suddenly smiled. "Oh, it's just a little girl."
"It's a little girl?" The second man asked, walking up and kneeling down to eye-level with Yuki.
"It's a little girl!" The third man happily said, walking up, and both he and the first man knelt down with the second.
"Is something wrong, miss?" The first man asked, and the way they were smiling at him made Yuki even more nervous.
He looked down at the ground and fiddled with his fingers, shifting around on the balls of his feet. "W-well, I got lost... and I don't know where I am..."
"Ah, so you need to find out where you are?" The man stood up, looking around for the street name. "I'm pretty sure this is-"
Yuki ducked down, covering his head just as a water balloon flew through the air and hit the man right in the chest, bursting apart on contact and dowsing the man.
He fell down onto his back, clutching his soaking shirt, his eyes wide open in shock.
"Takeshi!" The other two shouted, the second yakuza rushing up to his friend and grabbing his hand. "Stay with us, Takeshi! Keep yourself together!"
Takeshi gripped his friend's hand. "Jiro..." He coughed, and it didn't look like he was going to make it.
"What is it, Takeshi?" Jiro asked, leaning in closer.
"A-are my socks... dry?"
Jiro hurriedly checked his socks. "Yes! They're dry! They're dry, Takeshi!"
He smiled. "Thank... you..." With those last few words, his hand went limp.
"TAKESHI!" Jiro shouted, bursting into tears.
The third yakuza tightened his hands into fists and turned towards Yuki who was staring at his friends like they were idiots. "You brat! What did you-"
A water balloon collided with his head, sending him flying to the ground and knocking him out. "Haruto!" Jiro yelled, and he frantically looked around for who was taking them out. His eyes caught Yoshi peeking out from the corner, her slingshot pointed directly at him. "We'll remember this! You'll pay for what you did to us-"
Jiro fell on top of Takeshi, all three yakuza now soaking wet.
We actually did it! Yuki thought, smiling big and wide. He ran back to Yoshi and they high-fived, grabbing each other's hand and dancing around in a circle before facing the dazed yakuza. Then they started to sing.
"What do you think you guys are doing here?" Yoshi started.
"This is our town! You've got no business here, so go back home!" Yuki joined in.
"Yeah, back to your mommy!" They both exclaimed, smiling at each other.
"All the shop owners around here pay us the protection money~" Yoshi continued, Yuki turning towards her.
"Here's the money, ma'am." He said, placing a hundred yen coin in her hand.
"And we keep all the thugs in line!"
Yuki placed his hands on his cheeks. "Oh no! It's those twins again! We have to behave, or..."
"Or else!" They shouted together, stretching out their arms and clasping hands.
"You think you can take us on?" They sang together, in perfect sync. "You better know who you're dealing with!"
Yoshi stepped forward, Yuki holding her hand as he hid behind her. "I'm the great and terrible Yoshi, boss-lady of the Serizawa Family!"
They turned around as one, Yuki now in front, a blush on his face. "And I'm the cute and adorable Yuki, who can capture the heart of any boy or girl...!"
Yoshi stepped out from behind, the twins clasping both of their hands together as they leaned forward. "Together we're the Serizawa Twins, and we own this town!"
Yoshi leaned towards Yuki and planted a kiss on his cheek. "That was great, little brother."
He blushed redder. "D-don't do that where they can see, Yoshi-nee!"
She only giggled.
The three yakuza were sitting up, glaring at the twins. "Those brats..." Haruto muttered, rubbing his head.
"But you've got to admit..." Takeshi began, and they both looked at him. "That Yuki-chan is pretty cute~"
"...Yeah." They both agreed, blushes on their cheeks.