Soul

Yuri can't catch a break when it comes to his soul. In the first game he is cursed to lose it to the malice of monsters residing inside it; it's an exchange for his power of Fusion. In the second he gets hit with a curse called the Holy Mistletoe within about ten minutes of pressing "New Game". We later learn that this curse is one that drains the soul from its victim. Slowly but surely, the cursed's memories, thoughts, and feelings are all eaten away by the Mistletoe until they are nothing but an empty husk.

Needless to say, it's a real bummer. Yuri lived his life assuming he would one day lose his soul. It was his greatest fear to be overtaken by the malice of monsters inside of him and become one himself. Whenever he fused, the fear would resurface.

He thinks all the monsters he has fused with will devour his soul... "I don't want to turn into a monster!" he screams, every time he fuses.

After Alice helped him confront his fears and sacrificed herself in his place, these fears are laid to rest. It makes the Mistletoe doubly painful. The life that Alice gave him is now being whittled away, along with the things most precious to him: his memories of their time together and time with his companions. For someone like Yuri, this is worse than death. He is losing everything that he treasures and everything that separates him from the monsters he fuses with.

Rather than wallow, Yuri soldiers on to defeat Nicolai and repress his fears of the curse. But it haunts him and there are new residents in his Graveyard now: Jeanne, a young girl who died in Domremy, and a sleeping version of himself growing out of a giant tree emerging from the center of the Graveyard. It is the Mistletoe's shape in his soul. At first Yuri shouts at his other self to wake up. He feels helpless before the power of the curse. Over the game, he comes to feel close to the sleeping Yuri, "almost like a brother". The Mistletoe's curse is now as much a part of him as his Fusion ability; there is no denying or stopping it.

If the player makes the correct choices and receives the "Good" ending (good, relatively), Yuri chooses to die rather than let his memories be stolen from him. He fulfills his self-appointed destiny and saves the world (again) before allowing himself to be killed. Alice died to save his soul before and he dies to save it a second time.

The Graveyard

Yuri's soul, or maybe all Harmonixer's, has several peculiar properties. At least, I assume they are, and not everyone in the Shadow Heats universe can manifest their fears as a masked man to punch around whenever they feel like it.

There is a graveyard in his soul where the monsters he has slain in battle, and now fuses with, rest. There are tomb stones for each of the six elements in the game's combat system: fire, water, earth, wind, light, and dark. The malice of the monsters there grows until Yuri must cleanse it from his soul by going into the Graveyard and defeating them. This catharsis is removed in the second game; perhaps because Yuri has accepting his power of fusion instead of fearing it. Or maybe the developers just thought it would be repetitive.

The Graveyard also reflects Yuri's mental state. In Covenant his fear of the Mistletoe takes the form of a giant tree growing inside it, much like how in the first game his fears took the shape of Foxface. It's definitely a reflection of his subconscious. The parts I'm curious about are Jeanne and Alice. Does he really meet their souls or are they merely manifestations of his hope, an opposite number to Foxface? I kind of doubt even the game knows.