Get the Sister
The Sisters of Parvos are your own personal Corpus adversary similar to Kuva Lich system. Once you have completed The Call of The Tempestarii and The War Within you can get a sister. Just remember you can not have both sister and lich at the same time
to get a Sister you need to enter the Granum Void found on Corpus Ship tilesets. Better to equip Xoris. Use a Zenith Granum Crown at a Golden Hand Tribute and enter the Parvos Granum’s pocket of the Void to battle Errant Specters. By reaching at least Rank 1 within the Granum Void you will call a Sister. (Remember getting Protea)
The Sistem and hound will span on the ship once you are back from void. Now you can Mercy kill a Sister if you like the Weapon. As Kuva Lich, the Progenitor warframe will decide the Damage Type. Each sistem has its own Hound Pet.
Now when you go back to Orbiter you can see the name and details of the sister. The Sister will influence only one planet and the planet will change based on the levels, so that match-making is easier.
Fight the Sister
Once back in your Orbiter, the Sisters name is revealed and takes over the pre-existing Kuva Lich screen to display all her attributes, abilities, AND her trusty Hound. New to the Lich system these Hounds serve as the Sisters personal assassin, tasked with making your life difficult within the Sisters influenced Sector. Venus for level-1. Hound Mercy Kills can award you Requiem Relics!
Sistem will steal only Credits and each time you kill sistem you get some Credits and not Kuva.
Level- 1 is Venus, Level-2 is Phobos, Level-3 is Jupiter, Level-4 is Neptune and Level-5 is Pluto.
Once you use the correct sequence of Requiem Mods, she will flee to final, guaranteed showdown in her Capital Ship within Railjack in the Neptune Proxima (minimum Pilot Intrinsic 5).. So now you can prepare well and go to the speacial node. This also helps in match making with other players and kill the sisters one by one in the same mission.
The final fight is good, as you get to play Sisters, Hounds and Warframe Specters. Once you defeat the sister, you have the familiar decision to either Convert or Vanquish your Sister. Converting a Sister earns you back all stolen Credits, allows her to randomly join you in mission as an ally and becomes eligible for a Railjack Crew member (including On-Call)! Vanquishing your Sister earns you back all stolen Credits, the Sister’s signature weapon, Hound and Ephemera (if applicable).
Best part is you get additional Hound parts when you squad mates kill their sisters.