As a Void or Stasis subclass, collect Captured Void or Stasis Energy from defeated Hive combatants.
"Ikora said she needed a Void Guardian to handle a 'Hive problem.' Does that make you all the best at sword logic? No one's been able to explain sword logic to me in a way that's satisfying. For example, Shaxx fears me, but not because I'm stronger than him. How does sword logic account for that?" —Eva Levante