Starring up a gear will give it random stat boosts and bonuses, but nevertheless higher than the original gear. Only orange gears R4 above can be starred up. To Star Up a gear, you’ll need to use gears of the same class, quality, tier, and part. So in the example below, to star up the R7 Wardrum Top Wear, you’ll need another R7 Wardrum Top Wear that will be “consumed” and fused to get a 2-star version of the item.
If you’re starring up a 1-star gear, you’ll need another copy of the item and Star Crystals. This can be done until your gear reaches 4-star. Furthermore, 4-star orange gears can be further upgraded to a 4-star Red Gear with exceptional stats and CP boost.