To unlock Richtofen (Zombie Character) in Black Ops 4 Blackout, you need to play find the Letter to the Emperor, use it in the Blood Fountain to get the Blood Vial and complete the match in the required place. If you fail to complete the character mission for any reason in one match, you need to find the Letter to the Emperor and the Blood Vial in the next game again.
Richtofen’s mission item can be found in front of the Blood Fountain in Asylum after sacrificing the Letter to the Emperor in it (Asylum desk, Lighthouse desk,…)
HOW TO FIND AND COLLECT LETTER TO THE EMPEROR
To make the Letter to the Emperor appear, interact (X/Square) with the typewriter in one of the following locations. The Letter now appears on the desk and can be picked up by interacting with it.
HOW TO GET THE BLOOD VIAL
Take the Letter to the Emperor from the typewriter and go to the Blood Fountain in the center of the Asylum Building. After you interact with the fountain (X/Square) the Blood Vial appears in front of the fountain.
Once you have the Blood Vial in your inventory, stay out of the action and finish the place in the required placement (Top 5 in Solo)