Fastest character to seven stars?

those available in GW shipment, if you can clear GW everyday, it takes 22 days.
Otherwise, if you spend some crystals on refresh, those on cantina (nodes and shipment) can be 7stared in Under a month.
do both;

Unlocking Shard Shop btw, is not a huge advantage. I have had it unlocked for a while now, and I think I have only picked up one or two items from it. The costs, are huge compared to the shards you turn in for currency

Yes, but think about it, if you have an easy character grinded to seven stars, that means it's easy to get more currency for the shop. That's why I want an easy character

meh,
honestly mate, you will see what I am talking about once you open it. the exchange is beyond horrible.
can not remember how much currency you get per shard ( thinking maybe 15 ) but like two common to get shards ( from like Cantina, GW, Arena ) you are playing 300 for 2 character shards. For the hard to gets ( Grievous or K-2S0 you are paying 1k - 1.25k for 5 character shards )
Just trying to give you a heads up,
you are much farther ahead, farming shards normally, and working towards the rare ones over time with excess means

Jedi Consular, Chewbacca, and Talia. Some of the first characters you get access to and some of the first you can farm.