Gintama chad here, Varka has the same voice actor as Gintoki (the guy on the left) and if you know anything about Gintama its that Gintoki’s constantly being paired with the guy on the right.
You already know where this is going, they literally had a whole episode breaking the fourth wall where they admitted 90% of their DVD sales came from women. So don’t be surprised that Varka is popular in Japland