There are ranks in the game (Bounty Hunter, Super Hunter, and Elite Hunter) that appear near the WiFi connection button on the multiplayer menu. While Bounty Hunter is the default ranking, Super Hunter requires you get 40 points, while Elite Hunter requires you to get 140 points.

A simple way to get these points is to get two Nintendo DS units and do a multiplayer game from a single card (known as Single Card Play). Play any game and win a battle (Battle Mode is best because you can set the kills and time as low as you want). For winning a battle, you get one point (though if you lose, you lose a point). In this way, you can accumulate points easily to increase your character ranking.