I believe lyrics are shown to both the first opening and ending songs of the tennis anime, Baby Steps. Here is a partial shot from the ending:
You can see that the normal credits are single rows of characters. However, the lyrics at the bottom include a row of a few mini-characters above the main ones. What do these additional markings (characters?) indicate? I am not asking for a translation, just what their purpose is.
I vaguely remember seeing them in another series or two, but this is the first time they really caught my curiosity. I'm assuming right now that they are related to the music, perhaps how the song may have modified pronunciation of certain words. It appears too sparse to be some sort of full musical notation. There is only one voice in each song, so it is not the simultaneous words of a second singer.
In the English Wikipedia there is an article called Shakuhachi Musical Notation related to Japanese music. It did not seem to help, though I don't know much about the topic. (I.e. I didn't see any pictures showing the double-row lyric thing.)