Bivalvia Magic

 Bivalvia Magic (二枚貝マジック Nimaigai majikku) is a Holder Magic and a type of Spatial Magic used by Bivalvia Mages that involves summoning Sirens, magical beings with beautiful voices that reside in the Bivalvia realm.

Description
Bivalvia Magic is a type of Magic in which the user summons Sirens by singing a short verse, or calling them by their phrases, through the use of the pearl that the Siren resides in. It is a kind of Holder Magic, only that they are used to harbor a living creature in a vessel similar to a Lacrima. Each pearl contains a siren inside, to which all pearls interconnect with one another even if the siren lives in a specific pearl. Bivalvia Mages have the potential to obtain extremely rare Rainbow Pearls, which summon high powered sirens, and the more common, solid pearls, that can be found on beaches or sometimes inside of oysters; separating the pearls into two different classes. There are a large number of Solid Pearls, but there are only eight Rainbow Pearls. The Bivalvia Sirens have varying levels of power and a structured hierarchy based on such. There are the top three strongest, and then the rest are structured most powerful, to least powerful, normally the eight pearl.

A special attribute of the Bivalvia Sirens, is their possession magic, which makes them very dangerous. The user can wear the pearl and temporarily increase enhance their abilities, but, if they wear the pearl much longer than their magic power allows them to, they will gain the hair and eye color of the said siren, and their clothes will change to match the siren who has taken over their body.

Bivalvia Mages ability to summon however many sirens depends on how much magic power they have. The more powerful the siren, the more magic energy they exhaust. The more powerful Bivalvia Mages are able to simply sing the sirens verse instead of touching the pearl.

Contracts and Rules
When a Bivalvia Mage receives a Pearl and summons it for the first time, there are two kinds of pacts they have to make. The first one is a short temporary pact that lasts for a short while. After the temporary pact is made with the siren, they want a fight whether the new owner can control them of not. After the owner is proved to be worthy, then, a bilateral pact is concluded that lasts until the death of a contractor or the breaking of an alliance. The pearls the sirens reside in are known as "Bivalvia Pearls" or "Siren Pearls".

The Sirens are a bit more barbaric in their ways and rules. They have a leader, high queen, but there are little rules, and whatever rules there are, they generally aren’t enforced much. The Sirens are pretty much given free reign, but most have self-respect and try not to harm humans. It also takes a very strong willed Bivalvia Mage to control one. If one does become unruly, or any other reason, the user can simply crack the pearl, and it’ll either seal them inside forever, or they can swim into another pearl somewhere else, waiting for someone to summon it again.

Rainbow Pearls

 * Pearl of the Acoustics: Summons Tavia, the Echo singer. Leader, high queen.
 * Pearl of the Skies: Summons Fina, the singer of Storms. Second Strongest.
 * Pearl of the Telluric: Summons Nahauti, the Earthbound singer. Third in command.
 * Pearl of the Tinder: Summons Adena, the Scalding Singer.
 * Pearl of the Blight: Summons Pavati, the Bane singer.
 * Pearl of the Glacier: Summons Glyndwr, the Hailstone singer.
 * Pearl of the Lambent: Summons Haizea, the Luminous singer.
 * Pearl of the Ocean: Hydra, the Rain singer.

Solid Pearls

 * Pearl of the Tides: Summons Esme, the whirlpool singer. Resides within a purple pearl.
 * Pearl of the Hurricane: Summons Rezla, the Gale singer. Resides within a Blue pearl.
 * Pearl of the Reef: Summons Linda, the Coral singer. Resides within a red pearl.

Under construction

Spells and Abilities

 * Cracking Seal (クラックシール Kurakkushīru): This is not an ability to be taken lightly, as once the damage is done, it cannot be reversed under any circumstance. If the user wishes to, only they, can crack their own pearl with their magic energy. Which, if the siren isn’t fast enough, can either seal them within that pearl forever, or they can escape to the Bivalvia realm quickly and instantly get transferred to a new pearl.
 * Multiple Summons: Summoning more than one Bivalvia Siren uses up a lot of the summoner’s Magic ability which may even lead to their death. However, Bivalvia Mages can train and enhance their magical energy in order to accommodate to summoning a specific number of sirens. The most anyone has ever summoned at once was four. If one is capable of this feat, it provides greater flexibility as he/she is able to combine the strength and abilities of their sirens for more powerful attacks.
 * Telepathy: If the owner is wearing the pearl, sirens can communicate with their owner (via their pearls) without being summoned.
 * Self Summoning: Only Rainbow Pearl Sirens can summon themselves without the need of their owners. Solid Pearls don’t possess the power or magical ability to do so.