Facial animations broken on some (maybe all) characters

[Cleep2]

Describe the bug
Some facial animations (EM[CHARACTER_ID].GFS) seems to badly load for some models

Environment
Blender 3.6
Plugin version: 0.2.1 (also tested the latest dev)
Reproduced on P5R PC, P5R PS4 and P5 PS3 files.

To Reproduce
Steps to reproduce the behavior:

• Load any model for the character 0010 (Kasumi), For example C0010_01_00.GMD
• Load the facial animations for the model. For example EMT0010.GFS
• Activate the EMT0010 in the animation packs
• Load the animation 01
• This is what you see
  

I also tried that with Maruki (1014), Joker (0001) and they also have the 01 (and many other) broken. But Ryuji (0002) seems to not be broken (or less broken)

Notes:

• I also tested on original P5 (not royal) files and the same behavior happens.
• Not all the facial animations seems broken.
• I tried a lot of import parameters combination but none fixed the issue

Expected behavior
The facial animations works properly, for example Ryuji seems to work better

Files
Character models:

• C0010_001_00.GMD
• C0001_001_00.GMD
• C1014_001_00.GMD

Animation:

• EMT0010.GFS
• EMT0001.GFS
• EMT1014.GFS

Additional context
I think there might be an issue with the rotation of the bones, because when I tried to investigate I noticed that if I "swap" x and y rotation it "looks" closer to what I would expect for the "closed eyes". But I have close to no knowledge on quaternions so it might just be some coincidence.

[Pherakki]

Thanks for the report and sorry for taking a long time to react to this.
I'm pretty sure I know what the ultimate cause of this is... your note about a 90 degree rotation seeming to fix it basically confirms the thought... but I'm a bit worried that fixing this might be quite non-trivial.
I've done a preliminary investigation already but will need to dedicate some more time here to figure out why these bones seem to break the rules.

[Pherakki]

Thanks to DeathChaos the solution has been found: I'm using the wrong blend equation for Blend Animations.
Currently the plugin imports blends rotations using quaternion multiplication.
What appears to actually be required is to convert the quaternions to Euler angles and sum the Euler angles.

This will take a bit of work to implement because in addition to just importing as Eulers, I would also like to re-unify the scale blend animations with the position + rotation blend animations into a single animation now that everything should use the same blend method. This will need a little bit more work, so this will be on the list for the next release. Thanks for reporting this, it was a bit of a head-scratcher.

[Cleep2]

Oh glad to hear that you found the problem. And really happy that you will try to fix it in next release :). Good luck!