The upbeat and energetic former Jack's Chair, he is one year senior to Amu. As the captain of the Soccer Club, he is athletic and has good reflexes. He has graduated, which is the reason he has been replaced.
Once, in the school magazine, he and Amu are mistaken to be a couple, as a student got a picture of him holding Amu after she came out of her Character Change, and lost her strength. Saaya appears to have a crush on him, as when she saw the picture of him with Amu, she was furious.
Through the power of the Humpty Lock, he and Daichi managed a Character Transformation once, forming "Sky Jack." Daichi says the words "Kick, Stack, Trap and Shoot!" during a Character Change with Kukai.
At the end of the school year, Kukai graduates and goes on to middle school. However, Kukai returns to visit the Guardians from time to time.
He and Utau become good friends in both the anime and manga leading to a suspicious Yaya.
