Taichi

Mikey is a character of the day who appeared in The Battling Eevee Brothers (EP040).

All of Mikey's brothers fought over how Mikey should evolve his Eevee. Despite the fact that all of his brothers wanted to see him train an Eeveelution as well, he preferred keeping his Eevee just the way it was. However, he did not have the courage to tell his older brothers this. Eventually, after some advice from Misty, he decided to try anyway. His brothers eventually came to accept Mikey's choice after witnessing Eevee battle Team Rocket and emerge victorious.

(Source: Bulbapedia)