There are 6 styles, one's different depending on what version you have. The best place to fight viruses to get a style is DogHouseComp. (unless you already beat BeastmanV2, then you'll find V3.)

-Guts Style: Use your MegaBuster alot.
-Shield Style: Use Recovery, Gaurd, and Barrier chips.
-Custom Style: Use alot of dierent chips of the same chip code.
-Team Style: Use alot of MegaChips.
-Ground Style(White Only): Use chips like GrassStage, Repair, Geddon, and other chips that change the ield.
-Shadow Style(Blue Only): Use Invis chips alot.
-Bug Style: Put a bug in the NaviCust and battle with it.