I think Blender is lack of animation layer like in Maya. I dont want to use NLA. Is it so hard to add a layer system for animation? Or maybe is there any addon for this?
You must use the NLA! I’m sorry, but that’s the layer system!
You can always use actions as a type of layer. If you create an action by just clicking the new action without first clicking the X, it will populate the new action with the old actions keyframes. Just be sure to assign a fake user before you click the new action. You can then just “layer” the next series of keyframes on the new action and so on. AFAIK that is the only way short of using the NLA.