어야

have to, must

Sets up "only if this happens" — and followed by the verbs for "become" or "do", which is nearly always, it becomes the standard way to say "have to". Every example here is that pattern: I have to mention it, we have to take that road, these have to line up, you should use it with this. It fuses onto the verb stem, so the "must" sits in the middle of the word rather than as a separate word you can point to.