It was about as filler as they come.

I really can't stand how Mashrio and Yoshino have basically become devoid of emotion, so much so that someone else entirely has to beat some sense into them. It's sad to say that a character that is half comic relief is now more compelling than the main protagonists.

They keep saying in this anime that "The Tempest" is not a tragic story, but I think from the start of the story is already tragic enough learning that there is a dude/thing prisoned inside a tree for so many years.

so... people call "build up" and "development" filler now? I see.

I agree. It seems that some people here don't even know what a "filler" episode means.
The episode definitely has story development and people label it filler. We see that the truth is finally revealed to Yoshino and Mashiro, as well and we even see how some characters have grown, changed and we also get to understand some characters even more deeply due to the events in this episode. I admit it was a slightly slow episode but it is definitely not filler.

If it was an episode where they suddenly go to the beach and have fun etc. or whatever, then, I'll call it filler.

And here's the thing on what folks call "slow episodes"... it's all about telling a story. As long as the episode isn't like what's posted above and is anything related to the characters and/or the story. I'm fine w/o 24-7 action. I want a story and I've enjoyed this anime a lot. Curious to see how Yoshino, Mahiro, and Hakaze all fit in to this final battle; especially, Hakaze considering her connection with the Tree of Gensis and what that will or won't allow her to do to help.

The calm before the storm, or Tempest, if you will.

Now we can see why the episode was called Fuwa Aika. She's the glue that has ultimately made these people into a team that can beat the Tree of Genesis. Finally, they will all be working together instead of being suspicious of one another.

This was definitely not a filler episode.

First half started off good with the first 2 episodes, after that it got a bit boring imo.
Second half is so far amazing, just finished ep 20 and i'm tempted (haha) to see more

Blast of Tempest has become like fake gold to me. It looks good at first sight but , upon further inspection, you see it's not. Don't get me wrong. It's very entertaining and can be surprising. There were moments that had me in suspense. But it is no longer my favorite anime of the season. They start out with intriguing questions but I don't like the answer to those questions. I don't like the meaning behind the tree of Genesis and I'm still not sure if I got it right. I don't like the whole Aika explanation. It seemed to not make as big of an impact as expected b/c everyone was okay with it afterwards. Even though they addressed why they accepted it in the plot I still don't buy it. And because there was no drama and no impact, the frequent Shakespeare quotes just seem stupid in hindsight. I'm like what was all that for? Just trying to be deep? A good example of what I was expecting is The Sixth Sense. I expected, like that movie, Blast of Tempest had something specific in mind that would lead to something great. But it just added a lot of twists to a story that's really simple and not as creative as it let on.

So far I'm on ep 13 but I love the use of the hamlet and the tempest quotes

Dude!

Just when you thought the show couldn't get any weirder...

Since I havent read the manga and am just watching the anime, you cant be 100% sure if its not a tragic story. As both the tempest and hamlet are refrenced. Of course the show is called blast of tempest which might mean it wont be a tragjedy in the end. But tbh with how the show is I think it can end either way.

Again, I havent read the ending yet as im wanting to watch the last episode next week to conclude the series. So I understand I may be 100% wronge with what I just stated. Im not asking for any spoilers.

Ah I know right the pain!
Im now very tempted to read the last volume of the manga or some spoiler site to find out what happens. But I must not since I dont wanna ruin the last episode to a great series. Oh the struggle.