diff --git a/danmaku2ass.py b/danmaku2ass.py
index 556363b..e0fe406 100755
--- a/danmaku2ass.py
+++ b/danmaku2ass.py
@@ -303,8 +303,12 @@ def WriteCommentBilibiliPositioned(f, c, width, height, styleid):
                 styles.append('\\3c&HFFFFFF&')
         if from_alpha == to_alpha:
             styles.append('\\alpha&H%02X' % from_alpha)
+        elif (from_alpha, to_alpha) == (255, 0):
+            styles.append('\\fad(%s,0)' % (lifetime*1000))
+        elif (from_alpha, to_alpha) == (0, 255):
+            styles.append('\\fad(0, %s)' % (lifetime*1000))
         else:
-            styles.append('\\fade(%(from_alpha)s,%(to_alpha)s,%(to_alpha)s,%(start_time)s,%(end_time)s,%(end_time)s,%(end_time)s)' % {'from_alpha': from_alpha, 'to_alpha': to_alpha, 'start_time': delay, 'end_time': delay+duration})
+            styles.append('\\fade(%(from_alpha)s,%(to_alpha)s,%(to_alpha)s,0,%(end_time)s,%(end_time)s,%(end_time)s)' % {'from_alpha': from_alpha, 'to_alpha': to_alpha, 'end_time': lifetime*1000})
         if isborder == 'false':
             styles.append('\\bord0')
         f.write('Dialogue: -1,%(start)s,%(end)s,%(styleid)s,,0000,0000,0000,,{%(styles)s}%(text)s\n' % {'start': ConvertTimestamp(c[0]), 'end': ConvertTimestamp(c[0]+lifetime), 'styles': ''.join(styles), 'text': text, 'styleid': styleid})