The reason grian speaks Japanese in this is cuz
1. Real life grian was in Japan for a bit
2. I can speak it
Don't worry there will be translations lol
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"Griannn we have to go home!!" Scar yelled over the music. Grian didn't want to leave, but he was too drunk to stay. "But Scarrrr", "We're leaving, G" then Grian started speaking a language Scar didn't know,
"Watashi wa nokoshite shitaku ​​ arimasen"(i don't wanna leave)
"Huh-"
"Anata wa ijiwarudesu"(you are mean)
"Grian I don't know what you're saying-"
Grian grabbed Scar's shoulders in a weird attempt to make him stay. "Stand still really quick now"
"Uhhh okay?"
Grian got distracted, yet still spoke in that weird language,
"Uwa ̄ , anata wa kireina me o shite imasu" (wow you have beautiful eyes)

"Grian I have no clue what you're saying-"

"Urusai"(shut up/noisy)

"Grian-"

"Hansamu" (handsome/good looking)

"Grian I have no clue-"

"Urusai Kawaii otokonoko" (noisy pretty boy)

"Grian we gotta leave"

"Fineeee"

Scar took his hand and led him to the car, Grian complaining about not wanting to leave.

When they got home, Grian didn't stop.
"SCARRRRRR"

"Why are you screaming I'm right here"

"Oh.. haiiii" Grian made a face. Scar couldn't really tell what it meant, but he knew it wasn't good.
"Oh god- what?"

"Nani? Watashi wa mujitsudesu!"(what? I'm innocent!)

"Grian stop speaking in that language I don't understand"

"Anata no yōna kawaī otokonoko wa rikai suru hitsuyō ga arimasu" (cute boys like you need to understand)

"Grian I literally don't have a clue what you're saying"

Grian was upset, "Anata wa atsuidesu" he said slowly, hoping Scar might understand if he spoke slower. (You. Are. Hot. )

"Grian what the hell are you saying!?" Scar was losing his temper. He was also slightly worried.

"Ughhhh"

"Grian what?"

"You can't understand" Grian whined.

"Just say what you're saying in English!"

"I fucking love you asshole"
Grian gave Scar a dead-eye stare, which looked pretty funny considering he was drunk and sitting on the chair upside down.
"Grian! I thought you didn't swear!!!"
"Shut up Scar"
"Okay-"