単純にマテリアルをDoTweenでフェードさせる

MaterialFader.cs

namespace hoge.hoge
{
    using System;
    using DG.Tweening;
    using UnityEngine;

    public class MaterialFader : MonoBehaviour
    {
        [SerializeField]
        private Material[] alphaMaterials;
        [SerializeField]
        private string paramName;
        private float alphaVal;
        private Action onCompleteFadeOut;
        private Action onCompleteFadeIn;

        public void FadeIn(Action onCompAction = null, float delay = 0, float speed = 1.0f)
        {
            if (onCompAction != null)
            {
                this.onCompleteFadeIn += onCompAction;
            }

            DOTween.To(
                () => this.alphaVal,
                num => this.alphaVal = num,
                1,
                speed).OnUpdate(this.OnUpdateAlpha).SetDelay(delay).OnComplete(() =>
                {
                    this.onCompleteFadeIn?.Invoke();
                    this.onCompleteFadeIn = null;
                });
        }

        public void FadeOut(Action onCompAction = null, float delay = 0, float speed = 1.0f)
        {
            if (onCompAction != null)
            {
                this.onCompleteFadeOut += onCompAction;
            }

            DOTween.To(
                () => this.alphaVal,
                num => this.alphaVal = num,
                0,
                speed).OnUpdate(this.OnUpdateAlpha).SetDelay(delay).OnComplete(() =>
                {
                    this.onCompleteFadeOut?.Invoke();
                    this.onCompleteFadeOut = null;
                });
        }

        private void OnUpdateAlpha()
        {
            foreach (Material mat in this.alphaMaterials)
            {
                mat.SetColor(this.paramName, new Color(mat.color.r, mat.color.g, mat.color.b, this.alphaVal));
            }
        }
    }
}