Maybe make it a sister that was created by magic in an attempt to stop Annie's chaotic nature. This sister,lets call her Misty for now, has a more soft, calm, and kind nature to her unlike Annie. Misty uses ice and water, almost in a mist or fog like form, to combat her opponents. Anyways, Misty was made to befriend Annie, which she did, to calm Annie down. Annie and Misty were great friends when indoors, but hardly ever hung out otherwise. A big fight between Annie and Misty happened when Annie wanted to make Tibbers, greatly offending Misty in the process. After a short fight, Misty ran away from Annie, almost dead from the brawl. Soraka, being the healer that she is, found and healed Misty's wounds. Misty has learned some basic healing thanks to Soraka, and Misty now travels alone, looking for revenge on her so-called sister.
SKill idea (just thought of them so idk how they will be lol)
Passive/Calm Flows- When Misty suffers a blow that would normally kill her, she switches her empty health with however mana she currently possess. This has a 3 min CD.
Q/Choking Mist- Does mild magic damage to the target and nearby allies, blinds them for 1 sec and interrupts channels.
W/Restoration Cloud- Set an area that provides a healing circle for allies that enter it. It has high healing potential, but you must remain in it to receive the healing.
E/Defiled Fog- Does moderate magic damage to the target then adds an over time effect to the target. If the target dies while Defiled Fog is on it, Defiled Fog's dot will attach to the nearest champion.
Ult/Mysterious Shroud- Does major magic damage after a certain amount of time and silences all targets hit by it for 2 sec. Mysterious Shroud also disables all CC's on allies within its effect (but cannot be used during these effects)
What do you all think of the lore/skills? 