Just like normal relics, Requiem Relics may be opened in a fissure but not just any fissure as they require you to do specific ones called Requiem Fissures. You will be able to see the Requiem Relic in the item rewards section when your mission success summary is shown. Simply start a Kuva Siphon or Kuva Flood as you normally would and after the successfully destroying the Kuva Siphon and extracting you will either have a chance to be rewarded in Kuva Siphons or will have a guaranteed relic rewarded in Kuva Floods. Kuva Siphons have a chance to give you a Requiem Relic at the end of the mission while Kuva Floods are guaranteed to reward you with one. Requiem Relics may be acquired by doing Kuva Siphons, Kuva Floods and from alerts that appear from time to time.
Exilus Weapon Adaptors are used to open up the Exilus slots on your weapons for placing an addition Exilus mod to further enhance it.