I know this is an Elden Ring thread, but I'm going to take a moment to once again state that the protagonist of Bloodborne is actually the old man seen at the beginning of the game, and the blood transfusion process was essentially the creation of a new body for him to inhabit. The selectable player classes don't signify different backgrounds, but rather the progression of one person's life.

>Milquetoast - Ordinary, happy upbringing.
The player first started out with a normal upbringing, born to the Fishing Hamlet.
>Lone Survivor - Lone survivor of a lost hamlet.
The Hamlet had found Kos, and was subsequently invaded and butchered by Byrgenwerth.
>Troubled Childhood - Suffered misfortune in youth
The player was present for these events, which was obviously unfortunate.
>Violent Past - Terribly violent past. Rash, but stronger for it.
Obviously these events were violent, but they carried on nevertheless.
>Professional - Born specialist, fit for sleuthing or academia
Following this, the player actually joined with Byrgenwerth in order to learn more about the Blood and Eldritch Truth.
>Military Veteran - Experienced in war. A soldier with strength and skill.
They became a Hunter working under Gherman and Maria.
>Noble Scion - Scion to a respectable line with faith in your pedigree.
They betrayed their fellows in Byrgenwerth and brought the Blood to Cainhurst, as explained elsewhere in the game.
>Cruel Fate - Faced terrible hardships, but now confident in your purpose
In revenge, Cainhurst itself was invaded and wiped out.
>Waste of Skin - You are nothing. Talentless. You shouldn't have been born
At the end of their life, the player is reduced to an old man with nothing, necessitating the transfusion from the start of the game.