Apparently, the Omusubi character has a sort of mystery to it, where the merchandise will reveal information about them, in an enigmatic tone. For example, about Mentaiko and Tarako, the notepaper says, "This pair. Someone said they were sisters..." So where they say the "secret information," that refers to the little "clues" they have on the merchandise. (Thank you Sensei and Takao for helping me translate it!)

This pair, Mentaiko and Tarako. Someone said they were sisters...

Shisobou and Yukarichan are in fact siblings?!

Tenmusume and Tenmusu are twins!