(LEAD) BTS releases remix of 'Spring Day' to kick off celebration marking 5th year since debut
(ATTN: UPDATES with more details in last 3 paras; RECASTS headline)
SEOUL, June 4 (Yonhap) -- K-pop superstars BTS kicked off an annual celebration Monday to mark the fifth anniversary of the septet's debut by releasing a remix of its 2017 song "Sprin