Pronouns, in general. Japanese speakers leave pronouns implicit. Sometimes it's used as the source of sitcom misunderstandings.
Like, you don't have have to say "I want to go to the store" you can instead say, "want to go to store" and if you say it as a question, suddenly it's "[Do you] want to go to the store?"
We do that in Spanish all the time, with the caveat that our verbs already change depending on who performs them, rendering pronouns completely redundant a lot of the time