[Champion Concept] Lenette, the Light of Dawn
UPDATE 1 Changed Sunbolt to a small, ground target AoE (to make it able to be dodged) in the manner of Karthus's Q.
Increased cost of replacing Sunstones.
(Image is not my own. In just thought it pretty well represented the kind of design that would be appropriate for this character.)
Lenette, the Light of Dawn Primary Role: Mage Secondary Role: Support Ranged
Preferred Stats Mana + Mana Regen Ability Power Health Cooldown Reduction
Story The Solari have always considered themselves above the concerns of everyday Runeterra, preferring to tend to their rituals and worship of the Sun. Though each devotee is free to follow their own will - and many, such as Leona, do - they have preferred their isolation and quiet life above all else. But recent events an have caused upheaval that the Solari can no longer ignore. Ancient gods and civilizations stir in the sands, threatening to impose their vision of order on all they see. Void monstrosities prey on the weak and hopeless. Noxians threaten war at every turn, and Demacians rattle their sabers more and more to the tune of conflict. Heretical worshipers of the moon wander freely.
The Solari will no longer stay their hand. The time has come to show the demons, monsters and non-believers of this world the power of the Sun and her followers. And at the breaking of this glorious new Dawn will be Lenette, High Priestess of the Sun, to burn the impurities of the world away.
The Sun will rise, and it shall never set again.
Friends

Rivals

Design Philosophy Lenette, much like Leona, is designed to be the centerpiece of team's composition; dictating the flow of combat and thereby victory and defeat with powerful situation altering abilities that leave enemies burned, blinded and their attacks rendered deflected or rendered impotent. But while Leona is an in-your-face engagement tank, Lenette is designed more along the lines of Viktor or Morganna; affecting the battle with a well-placed spell or timed ability that disrupts or kills the enemy team. To avoid pigeon-holing her though, Lenette has a special item just for her that replaces her Trinket that buffs/changes her abilities depending on which form it takes. At the start of the game Lenette will need to make a choice as to what kind of stone she is going to take that game, because replacing the item is quite expensive.
Abilities
Passive - Powers of the Sun Lenette cannot use the standard Yellow/Red/Blue trinkets. Instead, she can choose from among three Sunstones that affect her abilities and her Ultimate in various ways. Replacing the Sunstone costs 800G to start, and the cost increases by 300G each time. Each Sunstone also grants Lenette a different passive.
Furious Suntone - Empower's Lenette's Sunbolt and Ward of Dawn, and grants her an additional %AP bonus.
Luminous Sunstone - Empower's Lenette's Wave of Light and Ward of Dawn. In addition, Health from items now grants additional bonus Mana Regen, and Mana Regen from items grants additional health regen, up to a cap.
Brilliant Sunstone - Empower's Lenette's Cleansing Light and Ward of Dawn. Grants Lenette an additional 1% tenacity per level.
Q - Sunbolt Instant Cast 12/10/8/6/4 second CD
Lenette strikes target area with a bolt of Sunlight (small AoE effect) after a small delay, causing X Magic Damage + Y magic damage (Y = %AP). Enemies struck by this ability take 1/3/5/7/10% more damage from Lenette for 1.5 seconds.
Furious Sunstone - If Lenette has more AP than her target, they are also stunned for .3/.5/.7/.8/1 second.
W - Wave of Light 1.5 second cast time 20/18/16/14/12 second CD
Lenette unleashes a wave of light in front of her. All allies it passes through are healed for X + (% total Mana).
Luminous Sunstone - If the wave passes through an enemy that is facing it, they are dazed for 1/2/3/4/5 seconds and take magic damage equal to X% of Lenette's total mana.
E - Cleansing Light Instant Cast 15/12/9/6/5 second CD
Lenette cleanses target ally of all debuffs/CC and prevents the application of debuffs/CC for .3/.7/1.2/1.7/2.2 seconds.
Brilliant Sunstone The cleansed ally receives a 1/2/3/4/5% movespeed, health, health regen and mana regen for every debuff/CC removed for 5 seconds.
R - Ward of Dawn Instant Cast 180/150/120 second CD
Lasts for 6 seconds. Lenette must channel the ability during this time. If Lenette dies, is suppressed or displaced, the ability dissipates early. Silencing her will not stop the Ward once it has been formed.
Lenette summons a spherical Ward of Dawn at her location. This ward blocks all ranged auto-attacks and all ranged abilities, excluding turrets and certain ultimate abilities (Vel'koz, Lux etc.). Allies who enter the ward receive a buff, depending on the kind of Sunstone Lenette is using. The Ward of Dawn is granted different properties depending on which Sunstone Lenette is using.
Furious Sunstone - Allies who pass into/out of the Ward are granted +25 AP and AD for 2 seconds. Attacks intercepted by the Ward reflect 30% of the damage back to the source; turrets excluded.
Luminous Sunstone - The Ward is now completely impenetrable and dissipates ALL non-turret ranged attacks it intercepts, including ALL champion Ultimates (including Vel'koz and Lux). Allies who pass into/out of the Ward receive +25 Armor and MR for 2 seconds.
Brilliant Sunstone - The Ward may now be placed anywhere within 4000 yards (range of Upgrade Blue Trinket/Pantheon Jump) of Lenette; Lenette must still channel the ability. Allies who pass into/out of the Ward gain +25% movement speed for 3 seconds.
(Numbers, specific abilities obviously aren't final and open to tweaking)
*Recommended Items *

Examples of Champions supposed to be Strong VS.

Examples of Champions supposed to be Weak VS.

Unique Interactions
(Same Team)
(Lennette): There is yet time to repent, my daughter.
: Never.
(Enemy Team)
(Lennette): You will pay for your heresy, child.
: I will silence your hatred, witch.
(Lennette kills
)
(Lennette): The Moon was always just a pale shadow of the Sun.
(Same Team)
(Lennette): Lead us to victory Leona!
: As you command, your Grace!
(Lennette Kills
)
(Lennette): Even the Void itself bows to the power of the Sun.
(Lennette, upon buying the item in question)
: I have seen many coins like this, brought in tribute by travelers.
: Such malice in this vessel. We shall cleanse this relic after the battle is concluded.
: Nothing can withstand the might of the Sun.
: Time itself is now my ally.