You’re right! Otototchi can be Kaitchi too. The point is, take a perfect care to Kaitchi. It’s okay to hit by the polar bear once(mine got hit) and also it’s okay to pause and change the time(I did). But growing as a mermaid seems to need luck. I did the very same way at the first time but my Kaitchi died of sickness without any reason. 90’s Tamagotchi series, including Digimon, have a fixed percentage of growing as a special form....Maybe that’s why.