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");
        }
    }