Comment by Sour Cinnamin on Serendipity

@Sour Cinnamin I'm back. Yisin (mc) has this condition where he doesn't age but because of it he could die anytime. Jintae was Yisin's housekeeper's son and his best friend, also they were in love but never really dated. Jintae was obsessed with curing Yisin's disease so he created this club "firebird" whose main purpose was to cure this disease. Now, we know Jintae is dead. There was an incident where Yisin ended up in a coma for a whole year and found out when he woke up that Seongtae got injured in that incident and Jintae was dead. Since then Yisin has been taking care of Seongtae.
Parallel to all this we got director Yoon (ml that we have not seen often). When Yisin was working for a company, another company went bankrupt and the CEO of that company died, later the wife commited suicide and their kid blamed Yisin for this. That kid is director Yoon.
Back to Seongtae. Now we found ot that Seongtae, director Yoon and Hyeop (his work buddy) all grew up in the same orphanage. And looks like Seongtae killed Jintae, burned the place down to bring him back to life and is mad with Yisin cause Jintae didn't come back to life, but Yisin somehow survived the fire. I think this is the incident where Yisin ended up in a coma and started taking care of Seongtae thinking he was a survivor.