Tae-min has a very distinct personality. And Woo-jin/Si-Woon loves him. So he recognized him. It's incredibly romantic, in my opinion.
Names:
Main character's real name: YOON TAE-MIN (Yoon is family name, Tae-Min is given name.)
Main character switches places with and assumes the identity of a guy who attempted suicide, named HAN SI-WON. (Han is his family name, and Si-Won is his given name.)
The twin brother of Han Si-Won is HAN JI-WOOK (Han is his family name, which is the same as Si-Won's family name since they are brothers, and Ji-Wook is his given name.)
The love interest of the main character currently refers to himself as MIN SI-WOON. (Family name Min, given name Si-Woon). He changed his name after moving away from his and Tae-Min's hometown. When he was a child, Tae-Min knew him as MIN WOO-JIN. Tae-Min still refers to him as Min Woo-Jin in his thoughts. But he always calls hi, Min Si-Woon, just as everyone else does. If he accidentally calls him Woo-Jin, he will blow his cover immediately.
The bad guy who organized Si-Won's gang rape on film after happily fucking Ji-Wook is LEE JOO-HOON. (Family name Lee, given name Joo-Hoon.)
Minty, The green-haired dude with a crush on Tae-Min is CHOI MIN-JUN. (Choi family name, Min-Jun given name.)
The tall, stoic, and handsome friend who keeps Min-Jun in line is LEE HOON (Family name Lee, given name Hoon).
Seriously, though, the closeness between the names Si-Won and Si-Woon, and Lee Joo-Hoon and Lee Hoon drives me insane. It's like the author is trying to fuck with us, lol! Hope this helps.
At the End of the Road