Quaternion.Inverse

public static Quaternion Inverse (Quaternion rotation);

説明

/rotation/の逆クォータニオンを返します。

using UnityEngine;

public class Example : MonoBehaviour
{
    // Sets this transform to have the opposite rotation of the target

    Transform target;
    void Update()
    {
        transform.rotation = Quaternion.Inverse(target.rotation);
    }
}