Fuyuki's Keronian partner is Keroro, even though Keroro is supposed to be his enemy. The two do share a natural curiosity (Fuyuki is drawn towards the mysteries of the world, while Keroro is mystified by things most humans consider commonplace), as well as the strongest friendship of the five Keronian/human child pairs. He affectionately calls him 'gunso' or 'gunso-san', meaning 'sergeant'. His appeals to their shared friendship are enough to stop Keroro's plans more than once. Fuyuki is delighted by all the wonders he gets to see with the keronians and jumps feet first in many of their plans.