In DBZ online, there is special equipment called 'Z- Artifact'. These equipment can further increase your Brawn, Agi, Con and Spi.
Unlike other equipment, Z-Artifact don't have level requirement. But to use it, Crew grade must be the same as Z- Artifact.
To obtain it, you must enter the Extreme challenge and defeat enemies there. Each Extreme Challenge stage set will offer different Z-Artifact set as reward.
Z Artifact can be upgrade both Level and Quality. To upgrade Z Artifact you need same artifact as it's material. In case you don't have same artifact, you can also use Z-Weapon Convert Talisman or gold
After reaching max level, Z Artifact's Quality can be improved. Once Z-Artifact's Quality improved, the upgrade Level will be reduced by 2 (so +10 Quality 7 Z-Artifact will become +8 Quality 8 Z-Artifact). You also need gold to upgrade Z-Artifact's quality
Z-Artifact Conversion
You can also convert Z-Artifact you own into another Z-Artifact. Keep in mind that only Lv 0 (not upgraded) Z artifact that can be converted. To Convert it you need certain amount of Z-Weapon Convert Talisman.