Note: The title translates to "Solitary Hide and Seek Envy", though there's a bit of a pun getting lost in translation here. From what I can tell, "Hitorinbo" comes from combining the word for alone (hitori) with the word for Hide and Seek (kakurenbo). Officially, it's just called "Solitary Envy".
Fun fact: The text that makes up the title of the song in the official illustration uses english letters to make the japanese characters. It's like the opposite of that fucked up coffee cup.