BTS are riding high. The Korean pop superstars and their Army have commandeered the Billboard Hot 100 in recent months: sending their single “Butter” to #1 for seven weeks, launching its follow-up “Permission To Dance” to #1 for one week, and then vaulting “Butter” back to the top this week. This has been partially the result of extremely dedicated fans purchasing certain targeted tracks week after week — an especially overt manifestation of an ongoing flaw in the current system, but also proof that BTS are a very popular act with a fiercely dedicated fan base. Their hits aren’t charting nearly as high in the UK, but their star power is such that a visit to BBC Radio 1’s Live Lounge today was still a big deal.