Glaceon was hatched as an Eevee in Time Warp Heals All Wounds from an egg May received from a day-care worker in May's Egg-Cellent Adventure. Since then, it has become a major part of May's team, watching every one of May's contests since it hatched.
Eevee made its contest debut in What I Did for Love!, where it went up against Brock and his Marshtomp. Although Marshtomp, being part Ground-type, could detect where Eevee was when it used Dig, Eevee eventually scored a win for May.
In Strategy with a Smile!, May used Glaceon in the finals of the Wallace Cup, where it went up against Dawn's Piplup. The battle concluded with Dawn as the winner, though Glaceon lost the match by only a few points. During this time, Dawn herself (when she first saw it) commented that Glaceon was very cute.
As an Eevee, it was playful, a bit kittenish, energetic and curious about the outside world. Also it showed strong loyalty towards May. After evolving, it becomes aggressive in battles, but is still loyal to its trainer.