Sandaime J Soul Brothers from Exile Tribe were on track to have the highest-selling album of 2015 with "Planet Seven," when Arashi swooped in and released "Japonism" in October. Arashi may have won this battle of the boy bands, but looking at the entire year — Sandaime may have won the war.

Two days before 2015 began, Sandaime nabbed the Japan Record Award for their song, "R.Y.U.S.E.I." The seven-member act bested the likes of chart-toppers AKB48, Southern All Stars and Kyary Pamyu Pamyu for the win. Soon after, they released their fifth studio album, "Planet Seven," which sold 508,337 copies on its debut. It topped the Oricon chart and didn't leave the top 10 until its 10th week.

The group also did well with its single releases. "R.Y.U.S.E.I." continued to sell well into the summer, even topping digital music store Recochoku's weekly chart in April. In September, the song was certified triple platinum for selling 750,000 copies digitally.