The Cocoon first appeared on the Tamagotchi Mothra as a revelation from the Mothra films. 2-3 days after Mothra Larva evolves into Mothra Grub or Batora Grub, it will not evolve into an adult, but instead evolve into a Cocoon, its body connected to the Eiffel Tower. After one hour the Cocoon will evolve into an adult. This matches how in the films, Mothra hatches from her egg as a Mothra Grub, then goes into her cocoon before emerging into her adult form, although one of four possible adults will emerge from the Cocoon in the Mothra Tamagotchi which will depend on Mothra Grub or Batora Grub's Justice Meter.
The Cocoon later appeared on the Mori de Hakken! Tamagotch, although this time the Cocoon replaces the teen stage as opposed to following it as in the Mothra Tamagotchi. Here, the Cocoon is named Mayutchi and is smaller as well as now resembling a peanut. Also the adult will evolve from Mayutchi after 24 hours, as opposed to one. It can also evolve into a variety of different adults as opposed to four. There is a new temperature function; there are four different Mayutchi, the one which Imotchi becomes will depend on how it is cared for after 2-3 days. For 24 hours, the player must control the temperature of the Mayutchi. A lower temperature will yield a "colder" character such as Funkorogatchi, while a higher temperature will yield a "warmer" character, such as Koganetchi. This does not apply if the spotted egg is selected; in this case the Mayutchi will become Kabutotchi, who cannot evolve any further. In all cases however, the player should keep the temperature fairly balanced; if the temperature becomes incredibly hot or cold, the Mayutchi will die. When attempting to obtain Helmetchi, an adult will evolve into Mayutchi a second time before becoming said character.