Unity uGUI のフェードアウト処理（ブログ公開用） https://nekonenene.hatenablog.com/entry/unity-ugui-fadeout-window

Fade.cs

using System.Collections;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

namespace Util {
    public static class Fade {
        public static void FadeoutObject(GameObject gameObject, float fadeoutSec = 2.0f) {
            if (gameObject.GetComponent<Fadeout>()) return;

            Fadeout fadeout = gameObject.AddComponent<Fadeout>();
            CanvasGroup cg = gameObject.AddComponent<CanvasGroup>();
            fadeout.Obj = gameObject;
            fadeout.Cg = cg;
            fadeout.FadeDuration = fadeoutSec;
            fadeout.Start();
        }
    }

    public class Fadeout : MonoBehaviour {
        public GameObject Obj;
        public CanvasGroup Cg;
        public float FadeDuration;

        float elapsedTime; // 経過時間

        public void Start() {
            StartCoroutine(fadeoutCoroutine());
        }

        IEnumerator fadeoutCoroutine() {
            EventSystem eventSystem = GameObject.FindObjectOfType<EventSystem>();
            eventSystem.enabled = false;

            while (elapsedTime <= FadeDuration) {
                elapsedTime += Time.deltaTime;
                Cg.alpha = Mathf.Lerp(1, 0, elapsedTime / FadeDuration);
                yield return null;
            }

            Destroy(Cg);
            Destroy(this);

            Obj.SetActive(false);
            eventSystem.enabled = true;
        }
    }
}