The resulting Devil Fruit, a fusion of the Flame-Flame, Quake-Quake, and Dark-Dark Fruits, could manifest in several ways, each with unique strengths and weaknesses:

Option 1: Inferno Quake Darkness

• Name: Yami Yurei no Mi (闇揺霊の実) - Darkness Tremor Fruit
• Type: Logia
• Abilities: This fruit grants the user mastery over a unique form of dark, fiery energy that resonates with seismic forces. They can:
  • Create and manipulate dark, fiery tremors: Causing devastating earthquakes infused with dark flames that can incinerate and shatter the earth simultaneously. The range and intensity of these tremors are controllable, from localized bursts to continent-spanning cataclysms.
  • Generate dark fire: The user can conjure and control dark flames that burn hotter and are more destructive than normal fire, capable of consuming even the most resilient materials. These flames can also be manipulated to create various shapes and weapons.
  • Dark Matter Manipulation: The user can manipulate dark matter, creating areas of intense gravitational pull or manipulating existing shadows to create defensive barriers or offensive attacks. This dark matter can also absorb kinetic energy, weakening attacks before they hit.
  • Shadow-Flame Constructs: The user can create constructs of dark fire, ranging from simple weapons to complex beings, all imbued with the destructive power of both flames and tremors.
  • Darkness Quakes: The user can generate powerful shockwaves that travel through shadows, bypassing physical barriers and striking from unexpected angles.

Option 2: Obsidian Inferno

• Name: Kurogan Ichi no Mi (黒岩イチの実) - Obsidian One Fruit
• Type: Paramecia
• Abilities: This fruit grants the user the ability to transform their body and surroundings into obsidian-like material infused with dark, fiery energy. They can:
  • Obsidian Transformation: The user can transform their body into a super-dense, obsidian-like substance, granting incredible durability and resistance to physical attacks. The obsidian can also be infused with dark flames, increasing its destructive potential.
  • Obsidian Constructs: The user can create obsidian constructs of various shapes and sizes, imbued with dark flames, for both offensive and defensive purposes.
  • Dark Flame Infusion: The user can infuse any object or surface with dark flames, turning them into devastating weapons.
  • Seismic Obsidian: The user can manipulate the obsidian to generate tremors and shockwaves, combining the destructive power of both elements.
  • Gravity Manipulation (Limited): Due to the density of obsidian, the user might possess limited gravity manipulation abilities, affecting the immediate area around them.

Option 3: Void Tremor

• Name: Kūhaku Shindo no Mi (空白震動の実) - Void Tremor Fruit
• Type: Logia
• Abilities: This fruit allows the user to become and manipulate a void-like substance infused with both dark energy and the destructive power of earthquakes and flames. They can:
  • Void Manipulation: The user can create and control areas of void, negating physical attacks and trapping opponents.
  • Void Tremors: The user can generate tremors within the void, causing devastating shockwaves that can ripple through space itself.
  • Dark Flame Void: The user can infuse the void with dark flames, creating a destructive force that consumes everything in its path.
  • Void-based Constructs: The user can create constructs from the void, ranging from weapons to shields, all imbued with dark flames and seismic power.
  • Absorption: The user might be able to absorb kinetic energy and convert it into dark flame energy.

These are just three potential interpretations. The specific abilities and characteristics of the resulting Devil Fruit would depend on the specific balance and interaction of the three original fruits' powers. The user's creativity and control over these powers would also play a significant role in determining the fruit's overall effectiveness.