The group debuted in the Japanese market after only two years since their Korean debut to further spread their activities and challenge themselves outside of Korea.[3] They released their Japanese single "Kokoro", alongside multiple versions, including one with all members and five featuring each member individually.[4]
Their lead track, "Kokoro" debuted at the 5th spot on the Oricon chart, and moved to 3rd spot the next day.[5] It was also chosen as an ending theme song for an anime entitled Blue Dragon.[6]