常にこちらを向かせる
https://gyazo.com/b4fc98c314302a46476e2f4d1f1649fe
Quaternion.LookRotationで簡単に作れる
code::
for(int i = 0; i < slides.Count; i++)
{
GameObject obj = slidesi as GameObject;
Vector3 relativePos = obj.transform.position - camera.transform.position;
Quaternion rotation = Quaternion.LookRotation(relativePos, camera.transform.up);
obj.transform.rotation = rotation;
}