How do you a Japanese o with the flat line over top?

You can't actually type the "o" with the flat line over top, as that character doesn't exist.

What you're likely thinking of is the Japanese character ō, which represents the long "o" sound. You can type it using different methods:

* Using a keyboard with Japanese input: Most Japanese keyboards will have a dedicated key for "ō". It's often found next to the "o" key and will be marked with the character itself.

* Using the Romanization system: In Romanization, you can type "ou" to represent the long "o" sound. For example, "Tokyo" would be written as "Toukyou".

* Using special characters: You can copy and paste the character ō from online sources.

Let me know if you need help with any specific text you want to write!