Jin (9yrs old) has lost his parents in a horrible plane crash, and he is going to live with their close family friend. Kim family has a 4 year old son whose name is taehyung. They encourage tae to make friends with their guest who is gonna live with them and they end up becoming very close (bestfriends).
Jin is a very ambitious person, & at the age of 18, he moves out of kim's family apartment & starts his life in the apartment his parents left him, and with the money that his parent left behind, he starts his own business. After 3 years, he's now 21 & owns 3 popular cafes in seoul, and is living a luxury life. At the same time tae is 16 and his parents decide to get a divorce. This breaks tae's heart but when both of his parents decide to leave him behind and leave to foreign countries for their careers, tae feels super lonely. Jin becomes his only family and tae becomes jin's. As they grow even closer, tae starts feeling some deep & undeniable emtions towards jin, but jin feels guilty to taint tae's soul.
Tae ends up getting a J tattooed on his heart, & when jin sees the tattoo, he understands how far they have gone with their emotions!