"Melt" is about a shy girl who is in love with a boy. In her pursuit of him, she gets her bangs cut and encourages herself to look cute, all the while hoping he'd notice . Her love is pure; she loves him not because she is in love with being in love, but because she genuinely likes him, to such an extent she can't even bring herself to look him in the eye and feels like melting to simply be with him.
Later that day, it rains. Since the weather report was inaccurate, the girl is caught off-guard; while she does have a collapsible umbrella in her bag, she thinks it too small. The boy therefore invites her to join him under his own umbrella. Heart pounding, she is so happy she could cry, because in Japan sharing an umbrella is a sign of shared feelings and is associated with couples. When they reach the station, she almost tells him to hold her because she does not want to leave him, and can not believe herself.
Multiple Fanmade PVs for "Melt" exist; most of them feature Miku as the protagonist, acting out the events described by the song. The "boyfriend" character is often represented by a faceless person (a technique often used to represent "Master", or the VOCALOID user).
"Melt" and its PVs are so popular on Niconico and YouTube that it has been featured in some Nico Nico Medleys, and has many covers and parodies both by live musicians and other VOCALOIDs.
With over nine million views, the original upload of "Melt" on Niconico is the second most viewed original VOCALOID song on the site, behind "Miku Miku ni Shite Ageru♪". It isn't quite as popular on YouTube, although one reprint of the 3M Mix of "Melt" has over five million views. This puts it far behind other VOCALOID YouTube uploads such as "Matryoshka" and "World is Mine".
The third and last official version of the song, which received an animated PV. It was also added on the major release of the Supercell album under Sony Music Japan, along with the song "Hajimete no Koi ga Owaru Toki".