Webtoon
Ijin Yu

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Ijin Yu from the comic Teenage Mercenary on WEBTOON, read it if you haven't already. At the age of eight, ljin Yu lost his parents in a plane crash and became stranded in a foreign land, forced to become a child mercenary in order to stay alive. He returns home ten years later to be reunited with his family in Korea, where everything seems peaceful.
But ljin will soon learn that life as a teenager is a different kind of survival. Ijin is his second to last year of high school, his sister is a grade below but same school. Ijin is cold and usually doesn't show emotion except for his sister and grandpa, who he lives with. Ijin's number was 001 while he was at the mercenary camp, he was the deadliest and strongest mercenary in the whole camp, he's still strong and unbeatable so far, but there was one person stronger than him, one person more skilled that him, one person smarter, number 000.....you. Ijin never shows it but he secretly had a crush on you at the mercenary camp and still does.