Ways Items could interact with Runes

Cookie Jar (Requires Biscuit Delivery Service) (Limited to one type of Healing Potion)

• Cost: 500 Gold
• Recipe: Refillable Potion + 350 Gold
• UNIQUE Passive: Upon eating a Biscuit, also restore 125 Health over 12 seconds.
• UNIQUE Active: Eat a Biscuit. If out of combat, share one with the nearest allied champion (both receive the full effect). Can hold up to 4 Biscuits. Refills 2 upon visiting the shop.

This item type would require you to have a specific Rune. It could also require you to have a specific Path instead (main or splash), so it would say 'Requires Inspiration Path' instead then.

It's a Refillable Potion upgrade for Support-ish champions that lets you store additional Biscuits you get from Kleptomancy or Biscuit Delivery Service and share them with nearby allies. Might scale a little too well into the late game because Biscuits restore % missing values. If your Tank is missing 3000 Health that's a pretty powerful heal ...

Blessed Blade

• Cost: 950 Gold
• Recipe: Long Sword + 600 Gold
• 10 Attack Damage
• UNIQUE Rune - Overheal: Grants the Rune Overheal. If you already have the Rune, increases the maximum shield value by +40 instead (can only gain up to two Runes from items).

This type of item would give you a specific Runes. If you already have the rune it empowers it instead. You can only get two additional Runes from items for balance reasons (good to have caps) and for clarity reasons because the two runes have to be added to your rune overview next to your champion portrait.

Blessed Blade would build into Bloodthirster. Bloodthirster's passive would have to be adjusted to accommodate that change. That creates a bigger divide between Bloodthirster and Death's Dance (you should buy Bloodthirster if you have Soraka for one).

Enchantment: Runic Echoes

• 60 Ability Power
• 7% Movement Speed
• UNIQUE Passive: Killing a large monster restores 15% missing Mana.
• UNIQUE Rune - Arcane Comet: Changes your Keystone to Arcane Comet. Arcane Comet works against Large Monsters.

This type of item would even allow you to even switch Keystones in game. Switching Keystones would create a chat message that tells everyone you did it, like with Unsealed Spellbook. It could share this passive with Luden's Echo still.

The idea is that you start with a safe Keystone like Aery or Unsealed Spellbook, or you start with Electrocute for more burst damage on your ganks. Then you can switch to Arcane Comet once you have your Rylai's, enough Cooldown Reduction and/or the teamfight are starting up and you're bound to hit someone.

Enchantment: Warrior

• 50 Attack Damage
• 10% Cooldown Reduction
• UNIQUE Rune - Absolute Focus: Grants the Rune Absolute Focus. If you already had the Rune, lowers the Health threshold to 60% and this item grants +50 Attack Damage or +70 Ability Power instead, adaptive (can only gain up to two Runes from items).

This Rune would interact with the item's stats. The build path might be a little bit weird for AP Junglers if they don't have enough money to buy it at once because they have to buy Caufield's Warhammer, but if you don't want to change your Keystone to Arcane Comet or you already have it you can get this instead for tons of Ability Power and 10% Cooldown Reduction.