Webakaza's was foreshadowed during the fight.
He also didn't get his backstory after he died because it was the reason he committed sewerside in the first place.
Webinitially introduced as a fairly evil character, akaza's backstory in the infinity castle arc reveals a different side to his character.
Akaza's life before becoming a demon, known.
Webshe was intricately tied to the tragic backstory of akaza, also known as hakuji, who was taken in by her father keizo as her caretaker.