Chuuya was threatened to join the port mafia and Shirase, Yuan currently don't know he joined the port mafia.

Chuuya was hiding for them at arcade but dazai shouted "Nakahara Chuuya" Yuan and Shirase heard and saw Chuuya. They ran to him and Yuan immediately held Chuuya's arm and he didn't pull away. You felt a bit of jealousy? And just glares while you see Dazai talk to them

damn it. She wasn't pulling away, Dazai notices your reaction and immediately said in a singing tone "ooh is somebody jealous jealous~?" that caught, Yuan, Shirase and Chuuya's attention. Chuuya smirked and pulled her even closer

Context: since you and Chuuya always fought he decided to make you even more jealous when he noticed, you, Chuuya and Dazai are A trio that always fights, annoy each other and pulls out pranks. Even though you just met each other, your favourite thing is to make fun of Chuuya's height and Dazai's bandages. But deep down you all somewhere care for each other but would never ever admit.