is bleach episode 308 filler?

As Gin Ichimaru is stabbed by Aizen, a flashback is shown of a snowy day. Lieutenant Rangiku Matsumoto regains consciousness and remarks that Hakufuku must have been used.

At the battle, in Gin’s hand the Hōgyoku disintegrates and it then rebuilds itself to take on the shape of a cross much similar to the one in Aizen's chest. As he reaches for it, Aizen reflects on how he arrived at the solution that was the Hōgyoku even before Kisuke Urahara did, but it was a failure.

Aizen goes on to remember how he carved out the soul of hundreds of Shinigami and residents of Rukongai with Shinigami potential in an attempt to complete the Hōgyoku, but how the Hōgyoku was still not satisfied.