Son of Doctor Daichi Oonishi, Yuuki allied himself with the Cybertrons after his father was kidnapped by Gigatron. Though he desperately missed his father, Yuuki befriended many of the Cybertrons and was a frequent guest at their headquarters, acting as a sort of cultural ambassador to help them understand Earth's societies and history. A bright child, Yuuki has learned a lot about archaeology from his father, though he possesses no special powers, beyond a startling knack for being right where he needs to be, in the middle of coincidental Destronger attacks.