ソースコード

public static class LineRendererExtensionMethods
{
    public static Tweener DOFade
    (
        this LineRenderer self,
        float             endValue,
        float             duration
    )
    {
        var startColor = self.startColor;
        var endColor   = self.endColor;

        return self
            .DOColor
            (
                startValue: new( startColor, endColor ),
                endValue: new
                (
                    new Color( startColor.r, startColor.g, startColor.b, endValue ),
                    new Color( endColor.r, endColor.g, endColor.b, endValue )
                ),
                duration: duration
            );
    }
}

使用例

lineRenderer
    .DOFade( 0, 1 )
    .SetEase( Ease.Linear )
;