Help me brainstorm a pure-magic-damage ADC

This is something I got a pseudo-"green light" from RiotScruffy on: an ADC who does purely magic damage, not physical. Sounds too weird, right? Well, I aim to make it work.

I have some skills prepped so far, but need ideas for fleshing out the kit. I'll provide a general design direction I'm using to help out.

NOTE! - Everything here is subject to change. Don't freak out if something looks broken!

EDIT: Updated! The ult is removed, but the kit now has a Q and E skill. Needs a suitable ultimate.

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#Mikoto, the Shrine Maiden

General Concept

Mikoto is a marksman Champion who does purely magic damage instead of physical, even with her basic attacks, yet scales off attack damage. Offsetting this powerful mechanic is that Mikoto cannot critically strike, though she gains bonus magic penetration from building crit chance (up to a cap). Mikoto excels at hitting multiple targets at once, pushing lanes and spreading out pain in team fights, but doesn’t do nearly as well as other marksmen in one-on-one fights.

For team compositions, Mikoto's presence can help out greatly in that she allows the top, mid, and jungle positions to all take physical damage dealers without making their entire team deal only physical damage. Mikoto would be able to cover the magic damage position excellently. She also serves as a powerful pusher and helps to round out AOE compositions with her ability to spread damage around widely.

P - Spirit Talismans

Mikoto’s basic attacks deal magic damage instead of physical damage, but cannot critically strike. Critical chance instead gives Mikoto % penetration against bonus magic resistance (this includes MR from runes, masteries, items, and buffs), up to a cap of 40%.

Q - Yin-Yang Orb

Mikoto lauches an orb that deals magic damage to the first enemy it hits, then bounces to the closest enemy up to 4 times. Each bounce deals increasing damage. Max. 5 targets struck. Can't hit a target more than once.

W - Purification Amulets

For X seconds, Mikoto gains increased attack speed and fires amulets out at up to 4 enemies near her primary target (similar to Runaan’s Hurricane), each dealing magic damage and applying on-hit effects.

E - Balancing Phase

Passive: Your basic attacks apply a mark to your primary target (doesn't include targets hit by your W) for a few seconds. You can only mark one target at a time. (An indicator also appears to show whether you are "far or close" to your target in relation to the active effect.)

Active: If you are further than X distance from your marked target, you blink a fixed distance toward it. If you are closer than X distance to your marked target, you blink a fixed distance away from it. In either case, you also gain Y% bonus movement speed for a brief time after blinking.

R - (undecided)

#Design Intents

• Mikoto is designed to be strong against crowds, but weak in duels.

• Lacking the ability to critically strike, Mikoto's single-target DPS is lower than other marksmen. She compensates for this with her ability to deal high amounts of multi-target damage.
• Mikoto is not meant to scale well with AP, but scales quite well with AD and AS.
• Mikoto is not to have any ability that can deal a % of an enemy's health, making her weaker against high-health tanks and fighters.
• Mikoto gives a team the ability to take several other physical damage dealers while having a marksman who can deal purely magic.
• Mikoto lacks burst capability, but her damage-over-time can be impressive, especially against multiple targets.
• Ideal items for Mikoto include Runaan's Hurricane, Wit's End, Infinity Edge (which gives her magic penetration instead of crit strike), and Bloodthirster. She does not want (or need) a Last Whisper, Youmuu's Ghostblade, or Black Cleaver.

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Who wants to pitch in?