A Support that happily builds a manamune early on would be cool.

Muramana is a big AD item cost effective enough for a support to build with their typical budgets that also has an awesome on hit effect powered by the champions mana. For a champion to want to build this item they need an ability that can be spammed once every 4 seconds while walking around early on in the game. The champion should ideally have and spec into as much mana as possible. Lastly attack speed is ideal for the on hit effect.

Creating a support that covers these bases is all it would take and in every other regard they can be a typical support focused champion. Make the Q a spammable point and click similar to Ezreals, or make it an E that gives a burst of movement and attack speed going on a shorter cooldown with the next auto much like a draven/vayne sort of ability. Just something that can both be tapped repeadedly after buying tear and assists putting out the items damage.

The champion could get alot of benefit from mana for the sake of their more supportive qaulities. Perhaps a combination of high mana costs and a mana scaling or two could be in order to encourage the Muramana with perhaps a Ice Born Gauntlet, Frozen heart, or dare I say an Essance reaver(given the spammable ability however it would likely be a sheen item unless the base AD had to be garbage for some reason). Perhaps sucha champion could give allies(only) a sheild that scales with total mana. If you wana go crazy it could scale with current mana producing a ridiculous sheild at full mana and near nothing as the mana lowers, just an idea. Or their could be a ridiculously expensive but effective means of sustian that warrants getting a tear asap to get through a presumably weak lane phase.

Attack speed could be implimented in many different ways. One idea in particular I like is a passive where the supports attack speed while attacking a champion is based some way on the attack speed of the highest attack speed ally attacking the same target. This way such support can get good use out of a Muramana but still need to prioritize protecting/working with allies to win fights. If it were absolutely necessary however, an Attack Speed steroid could be in the ult though I'd rather see such a champions ult be alocated towards supporting still. Point is built in/cheap attack speed is a non issue and can be placed in any way on the champion.

For me the novelty of useing a Muramana on a suppport without trolling is more then enough i would be pleased no matter the specific qualities, also there is Lux and Pyke so why not. Should such a champion be ranged/melee, hybrid into crowd control/echanchanting, higher/lower mobility, and be squishy/tanky. I dont particularly care so long as Muramana is effective enough to be meta on the champion.