FirstPersonCharacter itself does not have Blur component, but the GameObject attached to it does:
[SerializeField] FirstPersonController FPC; /// <summary>Your First Person Controller.</summary>
/// Option 1.
private Blur blur; /// <summary>Blur's Script.</summary>
/// Option 2.
[Serializefield] GameObject objWithPFCAndBlur; /// <summary>So you could get both components from this GameObject.</summary>
void Awake()
{
blur = FPC.gameObject.GetComponent<Blur>();
if(blur != null)
{ /// As a good practice, you should do null checkings, on cases like this.
Debug.LogError("There was no Blur attached to GameObject");
}
}