I surprised that Death didn't have a bigger role in the Sorrow games, especially in AoS (I don't really like to think of DoS as cannon due to the fact that it doesn't really impact the overall story). I mean I would think that he can sense Soma's dark power. I would have made it so that Soma encounters Death several times. The first time would be the following:
Death: Interesting. What is a kid doing in my late master's castle?
Soma: I'm not here by choice. Some how I was transported.
A battle begins.
D: You're pretty strong kid. I also sense that you have a dark power. Who are you?
S: My name is Soma. All I'm looking for is a way to get home.
D: Well Soma, I'll let you live for now.
The second meeting:
D: Still alive I see. You seem to have gotten stronger and your power is very familiar. Fascinating.
S: What do you mean familiar?
D: Your powers resemble those of my late master. How does a human possess them?
S: I don't know. I first became aware of my abilities when I came to this castle.
D: Is that so? I wonder... No, it can't be!!! I must be going, there are others in the castle to deal with.
Third encounter:
Soma arrives in a room where he witnesses Arikado and Death arguing
Arikado: What are you planning? Your master is gone.
Death: You forget the prophecy. I am waiting for the new master to ascend to the throne. I have already encounter a few individuals how may be the one. You are one of them.
A: Never!!! I'll never follow in His footsteps!!!
Soma: Arikado!!! What is going on!? What does he mean that you are one of them!?
A: That doesn't matter. You still have to do what I told you.
D: Arikado? So, that is the name you're using now. Interesting. Farewell for now.
S: What does he mean "the name you're using now"?
A: It's irrelevant. You just need to focus on getting to the throne room.
Forth encounter:
After beating Graham, but before the fight with Julius.
Death: So, I was right. You're the one. You're my new master.
Soma: I want nothing to with you. All I want is to return to the way I was before I came to this castle and go home.
D: You would abandon all this power? So, be it. We'll see if the next person will ascend to the throne. However, in the mean time. I will destroy you.
After the fight:
Death: Damn you!!! You could rule the world if you want too.
Soma: Sorry, but I have no interest in that.
The rest of the game is the same until after the final boss:
At the shrine game
Mina: You're finally awake
Soma: Are we back
M: yes.
S: Good.
Arikado: You did well. Yoko has been brought to a hospital for further treatment.
S: Now that it's over, I want to know everything: Who are you, really? And, why did it seem that you had encounter Death before? I was as if you two knew each other for a long time.
A: Fare enough.
Arikado transforms into his true form (Alucard)
Soma & Mina together: What!!!
M: So beautiful!!!!
A: This is my true appearance. My name is irrelevant. I am Dracula's one and only child. However, my mother is human. And, yes, I've known Death for centuries.
S: Then why not ascend to the throne?
A: I'm not evil and I don't want to follow in my father's footsteps.
S: What about Julius? Aren't you worried that he may try to kill you?
Julius: I won't.
S: Why?
J: He has been my family's greatest ally for centuries.
This is some of my thoughts that could have been used in AoS that would have given Death a bigger role. I'm thinking about writing a fan fiction of AoS using these ideas.