Who was Mr Fahrenheit? And how Jun was able to text him if he was dead?

No Jun didn't text him. I mean, from what I understand, Jun was more like feeling it. Like he knew this was what Mr. Fahrenheit would have said to him, after everything that has happened. Also, Mr. Fahrenheit was a middle school boy who used to talk to Jun in the past. Yeahh... Hope that was helpfull
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thank you

Welcomeee~(≧∀≦)