Your question:
What is the data format (type) of 9-axis combination data which
Motion Fusion processing in MPU-9250 sensor.
My answer:
This question is so difficult to answer because it contains so much content.
I understand that data format what you refer means how to communicate with the MPU9250.
MPU9250 communicates by I2C to exchange data.
Check MPU9250's datasheet for more information.
Please refer to the following link for information on how to control the MPU9250 in Arduino.
I has created a component called MPUSeries for those unfamiliar with hardware control in ARDUnity.
MPUSeries informs the rotation information by quaternion to Unity.