Fields

The PlayerInputManager script has Serialized Fields to reference the PlayerBrain it controls and choose which buttons it will use in the Input Manager. The Platformer Game Kit is currently only designed for a single Player, but this would allow it to support multiple players by simply giving them each different button names.

public class PlayerInputManager : MonoBehaviour
{
    [SerializeField]
    private PlayerBrain _States;

    [Header("Input Names (Edit/Preferences/Input Manager)")]

    [SerializeField]
    [Tooltip("Space by default")]
    private string _JumpButton = "Jump";

    [SerializeField]
    [Tooltip("Left Click by default")]
    private string _PrimaryAttackButton = "Fire1";

    [SerializeField]
    [Tooltip("Right Click by default")]
    private string _SecondaryAttackButton = "Fire2";

    [SerializeField]
    [Tooltip("Left Shift by default")]
    private string _RunButton = "Fire3";

    [SerializeField]
    [Tooltip("A/D and Left/Right Arrows by default")]
    private string _XAxis = "Horizontal";

    [SerializeField]
    [Tooltip("W/S and Up/Down Arrows by default")]
    private string _YAxis = "Vertical";

Update

The Update method simply checks each button and tells the PlayerBrain to attempt the appropriate action:

protected virtual void Update()
{
    if (Input.GetButtonDown(_JumpButton))
        _States.TryJump();

    if (Input.GetButtonUp(_JumpButton))
        _States.TryIdle();

    if (Input.GetButtonDown(_PrimaryAttackButton))
        _States.TryPrimaryAttack();

    if (Input.GetButtonDown(_SecondaryAttackButton))
        _States.TrySecondaryAttack();

    _States.Character.Run = Input.GetButton(_RunButton);
    _States.Character.MovementDirection = new Vector2(
        Input.GetAxisRaw(_XAxis),
        Input.GetAxisRaw(_YAxis));
}