Death attacking Soma, despite the latter being Dracula, makes sense as Dracula had the Crimson Stone which granted him the power to command Death, which is something that Soma lacks.
The second form of Chaos. It's a pitch-black orb with sky-high defense, only taking Scratch Damage until you weaken it by striking down the eyes at the sides of the room, and even then, it takes substantially less damage from your attacks than the statues of the first form did. It's almost like you're attacking a stone — in fact, when you do kill it, it sprouts cracks all over and shatters. Could it be that the core of Chaos is, in fact, the Crimson Stone that empowered Mathias to become Dracula in the first place? (It helps that Aria of Sorrow and Lament of Innocence were both released in the same year, so they must have been in development at around the same time, and IGA was involved in the production of both games.)
The Red Minotaur enemy is vulnerable to the Killer Mantle soul. In other words, you defeat an angry bull by waving a red cape at it.
What did Richter claim Dracula to have been doing? "Steals men's souls and makes them his slaves". That's a perfect description of Soma's Power of Dominance, a.k.a. the soul mechanic, and fittingly, the one to use it is Dracula's incarnation.
Why does Julius have abilities like the double-jump and the ability to walk underwater? Because he already went through Dracula's Castle and still has the items/relics which gave him those skills!
The design of Castlevania is quite different from its predecessors. It has bright colours, with the walls being mostly white, large windows everywhere to let the light come in, a lot of outdoors space, and a large private garden away from all the hustle and bustle. For the typical 21st century city dweller like Soma, doesn't that sound like the perfect house?
Let's look into it more deeply: a large front yard, a banquet hall for guests, a bright study, very comfortable private quarters, and the inner garden, all sound perfect for inviting over guests.
The garden deserves special mention: it is located right at the center of the castle, and to reach it you have to transverse increasingly dark and private areas. The garden itself has a lot of stonework and water fountains. These are all typical traits of traditional Japanese architecture, where the garden is considered the most sacred and private part of the house, and the deeper you go in the house the darker it is, due to Japan's (traditional) "let the shadow enter the house" philosophy. On top of all that, the music in the location has distinct Japanese tones.
It bears mentioning that the Arena, Underground Reservoir, Underground Cemetery, and Forbidden Area all lie underneath most of the brighter tones of the castle, as well as the Clock Tower and Top Floor areas being only reachable by hidden means or accessible only by Soma himself. These areas do not fit as parts that'd sound like something Soma, nor most 21st century dwellers, would want. But why are they there? Because in a sense, as much as the Castle changing to suit Soma's wants, it all still has the underlying tones that he's still Dracula deep underneath it all, and while Soma is in control, just the wrong step or going to the wrong place could end up bringing back Dracula in full force.
The Undine soul seems like a weird power to keep; judging by the fact that it's in a lantern, Dracula thought it was important. Couldn't Drac use a water breathing soul? We don't know if running water hurts Dracula the same way it hurts Alucard, and if it does, the water breathing souls might not nullify the damage. And since Alucard took the Holy Snorkel (which does protect from water damage), using the Undine soul to not get wet is a reasonable backup plan.
Soma is an Ordinary High-School Student at nineteen... wait, don't most students graduate from high school by eighteen? Getting Held Back in School is an odd character trait for someone as smart and good at problem solving as Soma is, except that he's likely inherited Dracula's perfectionism (holding himself back to improve his grades) and problems with authority figures (getting held back as punishment). Both interpretations are supported by his behavior in Aria of Sorrow; getting the True Ending requires leaving no stone unturned, and he's initially snappy to every stranger he meets, especially Arikado.
The Power of Dominance is full of horror if you think about it. What exactly could someone do with the power to enslave someone's soul and force them to do anything?
In Aria, when you check up on Mina at various points in the game, she denotes that she's not feeling very well, listing off various symptoms like her body feeling heavy, bad headaches, etc. But at the end of the game, she outright says they get worse, such as her limbs flailing about without her control or her randomly passing out. Consider that in pre-Igavanias, you're set on a timer to complete a stage. If the timer runs out, you die. That's what's happening to Mina, the Castle's influence is corroding and killing her! As for why it doesn't affect Soma, it's because he's Dracula. His own home wouldn't go against him anytime soon.
