How can I set a default pose for my character?

enter play mode

perform expected pose

pause play mode

copy character object in hierarchy

exit play mode

in hierarchy, delete old character object

paste copied character object in hierarchy, it will work

attention: ctrl+z and undo delete if you regret

create an animation file with your t-pose / default position you want the character in, and then name it so that it is alphabetically FIRST in your list of animations. Then, if the model doesn't get positioned to your liking immediately, re-drag in its prefab into the scene , and it should be posed as the first alphabetized animation you have on the fbx.

I was having a similiar problem, i needed my character in a t pose when dragged onto the scene, I changed his Animation type from Humanoid to None under the Rig tab in the model import settings. dont know if this helps

If you want the character to have the pose seen in the scene view, then while you're in there, drag the character from the scene and into a folder to transform it into a prefab. Now when you drag the prefab into the scene, the character should have the desired pose.

The method I know uses a state machine. First, animate a default pose (needs at least 1 keyframe). Next, import into Unity. After that, add an Animator Controller to your character. Open that AC (animatorcontroller/state machine) and drag your pose 'animation' in there (it should appear like an orange block. If it's not orange, then it's not default). You might want to configure an avatar for Mecanim while at it, but you don't have to.

Once you've followed those steps, every time you play, the character will start with your 'default pose'. Feel free to ask questions.