i dont know what to say about that... (●￣(ｴ)￣●)
I think either he was depresse becuz his plans always fail or its some kind of plot twist like "mr rose said to kill a fake but he didn't say which fake"
Well, never mind the last reason its just my wild imagination
I think it's because he couldn't manipulate or kill the other hyungs himself so he killed himself. Mr.Rose never said which one and he also didn't state that he can't kill himself. Now wether he is the real hyung idk but if it is him Doyung still what have deserved better.
Spolier
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One of the hyungs hang up himself
It's the purple one