"Begins ≠ Youth" character background infos from the Xclusive official website:
• Kim Hwan (19 years old) — A boy who moves according to his father's plan. He returns to Korea to help his father's election campaign.
• Min Cein (18 years old) — People think that he has killed his mother. An old piano that brings a memory with his mother gives him comfort.
• Kim Dogeon (17 years old) — A boy who want a normal life among sick father, unemployed mother and a brother who always get in trouble.
• Jeong Hosu (17 years old) — Abandoned by his mother in the amusement park and lives in the orphanage. He wishes that one day he will meet his mother.
• Park Haru (16 years old) — The pains disguised under the bright smile. He goes to mental hospital because of past memory.
• Kim Jooan (16 years old) — Exposed to drunk father's violence. He misses the moment that he once played baseball with his father.
• Jeon Jeha (14 years old) — Lives rich life than others, but he lives in a confusion with his stepfather and stepbrother.
[TRIGGER WARNINGS + SPOILERS]
Further comment contains sensitive details about their problems and mental illnesses:
• Kim Hwan — Suffers from his controlling father who has a suspicious past and he feels guilty towards his friends. (Spoiler: He travels back in time to save his friends from their tragic fates)
• Min Cein — Accused of killing his mother when she died by suicide in the fire. (Spoiler: He commits suicide by doing the same as her)
• Kim Dogeon — Suffers in poverty, works multiple part time jobs and lives in a container. (Spoiler: He got into a fight with a costumer and goes to jail)
• Jeong Hosu — Diagnosed with narcolepsy and munchausen syndrome after being abandoned by his mother in the amusement park. (Spoiler: He is overdosing with pills but dies on accident while losing balance in the hospital stairs)
• Park Haru — Diagnosed with PTSD and constantly has seizures after witnessing a child being tortured in the arboretum. (Spoiler: He commits suicide by drowning in the bathtub)
• Kim Jooan — Violently abused by his alcoholic father after his mother left. (Spoiler: He killed his father while protecting his sister and goes to jail)
• Jeon Jeha — Suffers loneliness from his abusive stepfather and stepbrother while neglected by his own mother. (Spoiler: He commits suicide by jumping off a building)
Disclaimer: These are all based on the fictional storyline in the music videos/short films/books by BTS. There could be changes in the drama's plot.