Place Nekrotafeyo Vault Key is an objective in the Story Mission, In The Shadow of Starlight in Borderlands 3
Return to Sanctuary
Go to Tannis' lab
Place Nekrotafeyo Vault Key
Take Nekrotafeyo Vault Key
Return to Desolation's Edge
Go to The Pyre of Stars gate
Place Vault Key
Enter The Pyre of Stars
Follow Tannis
Give Pandora Vault Key
Follow Typhon
Use Promethea pedestal
Use switch
Climb Eridian steps
Use Eden-6 pedestal
Go to Eridian geyser
Use Nekrotafeyo pedestal
Go to Tannis
Protect Tannis