Promise of Wizard was a promising anime that, unfortunately, has proved itself unworthy and has broken its promise. It's adapted from a game, and this adaptation leaves so much to be desired.
§ Overview
Masaki Akira finds herself, after entering an elevator, transported to another world. In this world, wizards face the so-called Great Calamity every year and Akira is the great sage for the year.
§ Notes
I. It's so frustrating that there are so many cast of characters. You barely know them. It's bad enough to expect to get to know an ensemble cast of 5 or 7 people within 12 episodes. But for 21 wizards? It's pretty much unreasonable.
Just look at the key visual. Can you honestly memorise their names and connect to their characters within 12 episodes?
Even worse, the narrative is so all over the place that you can't follow what exactly they are doing in a particular episode. Therefore, I'm not even sure if having 15 or even 24 episodes would help. It might help get to know the characters, but the narrative is hard to follow. This is the fault of the adaptation.
II. As for the premise itself within the game, I find it ridiculous. The Great Calamity is a yearly threat? It could have been better if the heroine's arrival means that the Great Calamity will be defeated once and for all. This yearly affair is no different to how Sisyphus rolls the same boulder only to roll back down again — ad infinitum.
We have a character who doesn't really develop into anything. She doesn't undergo training to unleash her latent powers. Her personality may be okay and may not be annoying, but what they did to her character is so frustrating.
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IV. It's also unfortunate that Mili's Year N, the opening song of the anime, is really lovely. 
It doesn't deserve this travesty. Her song and her musick would have been perfect for the upcoming anime, Secrets of the Silent Witch.
V. The original game is reportedly good, but with the way this adaptation sucked, not to mention I find the premise itself not compelling, I'm not gonna check out the game even if it's available.
§ Conclusion
This is an appalling anime that should have never been made. It deserves to be buried even deeper than the gutter. I am scoring it a 1 out of 10, the second anime this season that I scored that way, and this is one of the worst anime I have ever watched. Do yourself a favour and don't even contemplate watching this.