Fans are pouring into the historic heart of South Korea's capital for what may well be the year's biggest event: the return of the world's most successful band in recent years, BTS. Some 260,000 people are expected to turn up on Saturday at Gwanghwamun Square, where the seven K-pop stars - RM, Jin, Suga, J-Hope, Jimin, V and Jung Kook - will perform together for the first time since October 2022. Set against the backdrop of a 14th Century gateway to the royal palace, the band's one-hour set will include songs from their long-awaited new album, Arirang, which was released on Friday afternoon. For South Korea, this is more than the comeback of a K-pop band - it's also the return of a cultural force that has propelled Korean soft power with its record-busting mix of punchy pop and electric dance moves. Only about 22,000 people who managed to get free tickets will enter the concert venue - a smaller area in Gwanghwamun Square that has been cordoned off.…