Sirenmon is a Demon Lord Digimon whose name and design are derived from the mythological Sirens, her design is also derived from the mythological Mermaid. She is one of the members of the Royal Family, most notably the second child of Queen Majestymon and King Royalmon. Her twin brother is Valentinemon. She is also the older sister of Metaldramon/Signamon and Princessmon. She was created around the time the Digital World was in its infancy.
As one of the princesses of the Digital World, she is greatly respected and feared among many Digimon. She's often compared to her twin brother, Valentinemon, in terms of leadership, power, and appearance. When her parents were dethroned by the Celestial Digimon, Sirenmon and her siblings were forced to retreat to the Dark Area, where they were looked after by the Seven Great Demon Lords until they were reunited with their parents; also due to the allegiance the Royal Family had with them. She is also known as one of the most beautiful Digimon, rivaling that of her younger sister Princessmon. Due to the hierarchy of the Royal Family, Sirenmon also has command over many Demon Lord, Devil, and Fallen Angel Digimon; she also has command over the Elemental Gods, with the exception of her brother. Sirenmon is the only one of the Royal Family to be directly Cetusmon, the God of Water. While the army she controls are mostly the "Nightmare Soldiers", she also has power over the "Deep Savers". Among her henchmen, Sirenmon has GigaSeadramon and NeoSeadramon serving as two of her many lieutenants with other Digimon such as MetalSeadramon and MarineDevimon serving as attack forces. Like her siblings, she too resembles a human teenager, with the exception of her winged fins and mermaid-like tail. Like her siblings, she can retract her winged fins and tail inside her body. She also has the ability to transform her tail into two human-like legs and shift her tail's position as well. Her outfit resembles that of the one worn by Dark Phoenix in the X-Men comics.
- Possession – Like her family, Sirenmon is able to merge her body and overshadow or otherwise control another life form. While she has some strength of her own, Sirenmon's combat abilities are best suited to exploiting the full potential of a host body. It appears that when she has chosen a permanent host, she begins to alter the host's appearance to mirror her own (as evidenced by the appearance of Yoshino). After possessing a host, Sirenmon combines their power with her own. She also gains the ability to assimilate the techniques of those who she has possessed. Sirenmon uses this to take control of. Sirenmon uses this to take control of Sora Takenouchi and Yoshino "Yoshi" Fujieda.
- Death Beam - She extends her right arm and fires a small, thin, very fast, and concentrated laser-like beam from either her index finger or her tail, which barrels down and pierces through an opponent.
- Power Up - She has the power to suppress and increase her power.
- Telekinesis – She can lift or move large objects through the air and blow up objects as big as mountains with only her mind.
- Barrage Death Beam - A rapid-fire version of the Death Beam technique.
- Explosive Wave – She bursts out energy from all over her body in order to repel the opponents around her.
- Super Explosive Wave – A stronger version of the Explosive Wave, she releases a gigantic wave of energy from her body, causing a huge amount of destruction.
- Finger Beam - She holds out her index finger and releases an energy beam from her fingertips.
- Scatter Finger Beam - She leans forward and points all five fingers of her right or left hand, then she charges up five small golden-yellow energy spheres each on the tip of each finger and finally fires the energy spheres inflicting a great deal of damage.
- Tail Attack – She can attack her opponents using her powerful tail.
- Freeze Storm - A team attack used by Valentinemon and Sirenmon. First, Sirenmon puts her left hand in upward, making energy appear. Valentinemon soon joins her, and the energy grows bigger. When it is fully charged, they unleash the blizzard at the opponent, making the opponent swirling away in pain.
- Continuous Energy Bullets or Continuous Energy Waves - She fires many energy waves from a single hand at once at a very rapid rate, which causes a lightning speed effect.
- Galactic Donut - Sirenmon executes this attack by raising her index finger into the air and circling it above her head to create a yellow ring of energy. Once created, she transports the circular energy ring over her opponent, then lowers and homes it on them. This results in the opponent being gripped and trapped within the circular attack.
- Magic Materialization – Used to create clothes for herself.
- Shape-shifting – Her and her family have the power to shape-shift into any human and Digimon they have come into contact with.
- Eye Lasers – A thin laser-like beam is shot from both of her eyes.
- Super Siren Strike - To perform the attack, Sirenmon raises her hands in the air and charges white-colored energy on her hands. Then, she releases the energy in a form of a giant, white energy sphere and hurls it towards her enemy, inflicting a huge amount of damage.
- Telepathy – She has the ability to channel one's thoughts to another being.
- Titania Barrier - A blue-colored energy barrier is formed that protects her against upcoming attacks and projectiles. Sirenmon can also use this technique to create a powerful explosion capable of destroying its surroundings.
- Rapid Energy Cannon - Sirenmon expels multiple orangish-yellow energy spheres and guides them towards his opponent, creating a huge explosion.
- Divine Cascade - Sirenmon launches blue-colored energy beams surrounded by a rushing surge of water capable of causing major damage and can flood several block of a city.
- Tsunami Blade - She creates a trident using Magic Materialization and she uses it in combat to fight against her opponents. The trident is blue and silver in color it can be used as a spear and a sword to swiftly slash or impale in many directions, capable of piercing stone and steel. The trident can also control and manipulate any form of liquid and unleash power energy attacks.
- Pearl Crystals - She lifts both of her hands up and unleashes red and purple energy spheres from each hand at the opponent, inflicting lots of damage.
- Jade Trident - A variation of her Tsunami Blade, also created from Magic Materialization. The trident has an icicle-like appearance, silver and pink in color with the bottom resembling a corkscrew or a drill. She throws her trident at her opponent with extreme speed. As it travels through the air, it begins to spin and build up energy, forming an energy barrier. When it reaches its target, it acts as a drill, inflicting extreme piercing damage.
- Gigantic Spike - Sirenmon grabs the opponent's head and flies down to the ground as she drives the opponent head-first into the ground or a wall, resulting in an earthquake and inflicting a massive amount of damage.
- Moon Snow Sword - She creates a sword that is completely white with a hollow snowflake-like circle, and a white ribbon forms from the pommel The blade glows, and she makes a slashing motion when her target is in position. When she does this, the tip of the blade unleashes white-colored frozen energy discs. The attack not only freezes the ground, but everything surrounding it.
- Crystal Blast - She can unleash an avalanche of ice from her hand that can generate and fire ice shards and crescent-shaped blasts of ice at her opponent by swinging her arm in an arc at them.
- Mystic Shooter - First, Sirenmon raises both of her hands backwards, and charges red streaks of electricity in her palms. Then, she swings her hands over her head and fires reddish-pink energy discs against the opponent, inflicting a high amount of damage.
- Creature Creation - Using Telekinesis, she can create creatures made of water, ice and snow including dragons and golems, each one having access to her attacks.
- Ultimate Wave - She creates a vast, green energy sphere that, upon contacting with the ground, produces a powerful shock wave that travels in both directions from where it hits, inflicting great damage.
- Negative Power Rain - Sirenmon punches and kicks her opponent into the air, then fires nine energy blasts down at them.
- Gigantic Hammer - First, Sirenmon strikes the opponent down with a massive clothesline. Then, she grabs the opponent by their shoulders and picks them up to vertical kick them up into the air. Next, she teleports in front of the opponent as she grabs them by their head and flies down to smash them across the ground. Finally, Sirenmon picks up the opponent by their head, and uppercuts them in the stomach, knocking them away up into the air, inflicting a huge amount of damage.
- Grand Smasher - First, Sirenmon raises her hand toward the opponent and forms a big, bright-green energy sphere. Then, she fires the attack at her opponent by drawing her hand a little backwards, only to thrust it forward at high speed. The Grand Smasher flies at the opponent in form of a big, green ball with a short, green flaming tail, inflicting a huge amount of damage.
- Aqua Rings - Water droplets form around Sirenmon's body, and they combine together to create three rings of water that surround her body, or a large ring of water appears around Sirenmon and expands, healing her. She is able to use this on other Digimon and humans.
- Aqua Tail - Sirenmon's tail glows light blue and she spins it around. When she does, a spiral of water spiraling around her tail. She then flips around and hits the opponent with her tail.
- Blue Wave Shark - Sirenmon can use either her Tsunami Blade, Jade Trident or Moon Snow Sword to condense large amounts of ice, snow or water around her blade before firing it towards her opponent in the form of an energy blade resembling a shark tooth. She can fire multiple blasts in rapid succession with relative ease. The blasts strike with enough force to demolish houses.
- Neptunian Beam - A blue energy orb forms in Sirenmon's mouth. She then shoots multiple amounts of blue energy spheres at the opponent from the blue orb. When the attack is over, the last sphere explodes and sends the opponent back.
- Atlantean Sphere - Sirenmon's hands become surrounded in light blue energy orbs. Then, she fires the orbs at the opponent. The orbs turn into a huge pulse of water when they make contact with the opponent.
- Aurora Wave - She releases a shining metallic silver orb from her mouth which once fired turns into a powerful multi-colored beam at the opponent.
- White Mist - Sirenmon creates a white mist with her hand. The mist can absorb energy from the surrounding area, increasing Sirenmon's power.
- Burning Attack - Sirenmon performs a series of rapid arm movements before placing her palms forward, with the thumbs and index fingers touching each other to form a diamond shape. Then, she fires an energy sphere from his palms towards the opponent.
- Tundra Beam - A white energy orb is formed in front of Sirenmon's mouth. Light blue energy beams are then fired at the target, freezing anything it touches, or Sirenmon forms an orb of light blue energy in the palm of either hand. She then fires multiple light blue beams of energy from the orb at the opponent, freezing them.
- Blizzard Orb - Sirenmon opens her mouth and creates a energy orb surrounded by ice that shatters and releases a blizzard when she launches the attack at the opponent.
- Ruthless Blow - She charges towards the opponent at high speed, then she uses rapid movement (disappearing from the opponent's line of sight). The opponent suddenly feels a stabbing pain, and discovers to their shock and horror that Sirenmon has thrust her hand/palm into their back. Sirenmon ends the attack by pulling her hand out of the opponent's back and letting them fall helplessly to the ground.
- Planet Burst - First, Sirenmon raises one hand in the air and gathers her energy in the form of a giant, bright-pink energy sphere. Once it is ready, she launches the energy sphere at the opponent, inflicting a huge amount of damage. It is noted that in its first use, it is strong enough to blow either the Earth or a giant portion of the Digital World up at least ten times.
- Destruction Sphere - Sirenmon creates two medium-size flaming energy spheres in her hands and brings them above her head to create one single energy sphere resembling the Sun, which she throws at his opponent.
- Big Bang Crash - First, Sirenmon extends her arm, opens her palm and turns her hand up at a 90 degree angle. She then powers up and fires a powerful red energy sphere at the opponent creating an enormous explosion, inflicting a high amount of damage and even creating a large red dome of energy upon contact.