"Tohoku Evolved", one of the boss songs in X3 vs 2ndMix, while famous for being hard and for its shady Last Note Nightmare, becomes heartwarming when you learn that it's a dedication for the 2011 Tohoku earthquake and tsunami. There is the soundbite "with you" that is heard throughout the song, there's also the fact that you can't access the song if you turn on the "Wave" option on the preceding Extra Stage. However, the real kicker comes when you clear it: instead of showing the normal "Cleared" message, "Pray for All" takes its place. The message is still displayed for the song in the following games.
"Graduation (Sorezore no Ashitanote For each tomorrow)", which is also the official credits song for Extreme. It's a bit of a Tear Jerker as well; the song is about someone who has just graduated and feels nostalgic of all the things she likes at school, but nevertheless is determined to continue to step forward for an uncertain future while treasuring all the good memories. Considering that Extreme used to be thought of as the Grand Finale, the song also doubles as a send-off from the gamemakers to cheer up the fans who mourned the apparent end of the series.
TAG's song commentary for Over The "Period", where he basically rebuked the strangely long-persistent rumors that DDR is going end, even lampshading the tendency for people to think Extreme was the true end of the series, to the point that he created the song as a followup to "MAX. (period)" (which made its first arcade debut in DDR 2014) just to prove that DDR is not going to end. He then complemented this by stating his pride at seeing players slowly clearing the song as a Perfect-run Encore Extra Stage, saying that he knew no matter how hard a song is, some expert players would eventually clear it.