After the agony I went through trying to remove my On's faceplate following a tutorial that suggested prying from the front, I found a much better tutorial here. Instead of prying from the front, the Tamagotchi just need to be disassembled and the front half of the shell squeezed, as the link details. It's damage-free and I wish I had this earlier as my On's faceplate is damaged (thankfully, washi tape can hide that).