Meru

Meru is prince of the Deep Sea, destined to marry Natsumi Hinata, whom he claims to be his princess. Growing up with no memories of his childhood, family, home, nor race, he and Maru (マール, Maaru?) as his servant develops a second childhood, filled with loneliness. One night, Meru and Natsumi the kingdom's sacred weapon to uphold their titles with the Mer Ball, a weapon that resembles the Kero Ball. Kululu then reveals that Meru and Maru came from Maron, a planet of water, and Meru would eventually flood Pekopon to become his world. They were saved by the Keroro Platoon together with Fuyuki and Momoka.

With the corrupted Mer Ball forever out of the wrong hands, Meru and Maru ultimately fall in love and wish their friends farewell as they start a new life on Maron as prince and princess. Source: Wikipedia