((I have never made a Summon before, so I'm a bit fuzzy on how to go about this, but here's my first attempt.))
Name: Children of Light
Race: Photon Subjects
Description: Kairi bows her head and clasps her hands together and gathers light around herself. For a moment she seems to glow. Then the ground glows, no further than 20 feet from herself, and from the glows rise up to 10 Photon Subjects (akin to Heartless, but formed completely of Light). They look very much like the Heartless Shadows, but they are pearly white, distinctly feminine, with piercingly bright blue eyes.
Purpose: Kairi summons the Photons into battle as an offensive force under her command. They can serve as a defensive wall around her, after a fashion, but only so far as warriors would protect the one they serve. They can attack; they can throw themselves into the way of an attack. They cannot call magic, being purely melee combatants, although their melee attacks are infused with elemental Light energy.
Origins: Darkness is primal and basic. So is Kingdom Hearts and the Light held there. As the embodiment of Light, being born completely without Darkness, Kairi is linked to a power as fundamental as the Darkness that threatened to completely swallow Riku. Each primal element has its servants. For the Darkness are the Heartless. For Nothingness there are the Nobodies. For Light and Kingdom Hearts there are Subjects. Just as Riku was able to summon and control the Heartless when he surrendered to Darkness, Kairi is able to summon and control the Subjects because of her connection to the Light that created them. This basic level summon calls the smallest of the Subject creatures to her, the Photons.