About the "Enpty" thing, ever notice how some people spell it "senpai" and others spell it "sempai?" That's because, despite there not being a solo "m" consonant in Japanese, it sounds like an "m" when spoken. This happens because there is a solo consonant "N", where as the rest of its phonetics are a consonant and a vowel or a solo vowel (e.g. se, pa, i, etc.) and when going from an "n" sound to a "p" sound, it's like an "m" snuck in there when speaking normally because of how your mouth moves. So, the mangaka just got mixed up when trying to use English, no different from choosing wrong between "L" and "R" or "hu" and "fu." There's your random useless Japanese phonetics lesson for the day.