蛙って、よく見るとかわいいと思うの

Kaeru tte, yoku miru to kawaii to omou no

You know, frogs are actually pretty cute now that I’ve had a good look.

This use isn’t exactly specific to Aqua, but since she’s best girl I figured I would include her here. If we break down the Japanese to be extremely literal, we’ll get…

蛙って、よく見るとかわいいと思うの

Kaeru tte, yoku miru to kawaii to omou no

Speaking of frogs, a good look (+ connecting と to particle) think that cute (+ explanatory の no particle.)

Nowhere in that sentence is any word mentioning the speaker. But due to context of the previous few seconds of what happened, (she punched a giant frog) and then the fact that Aqua is using an explanatory particle when referring to thoughts, it just makes sense that she would be the one thinking them. That makes using any form of “I” redundant. In fact, when people say whatever word they use for “I” too much, they can come across as not caring about other people or really only ever wanting to talk about themselves. It’s a pretty big trap for learners actually, and it’s usually a good idea to make it a challenge to use them as little as possible.

Which do I use in real life?

Use one until your native friend tells you you sound funny and to use some other one instead. It’s okay to make mistakes, you’re a learner. I think people tend to get caught up in which one they should use a little too much, at least I know I did.

This isn’t to say that there isn’t a bunch of nuances in using one over the other, but that this is the kind of thing you’ll get used to and will make more sense the more you see them used along with what situation they’re used in. Pick one you think makes sense (If you’re a learner, you’ll probably want watashi if you’re female, and males will probably be going in between ore for close friends, and boku and/or watashi for when they’re using any formal/polite speech.)