Junior
One's Junior
noun
The comrade who's behind you is your junior.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. The reading for 後 is the long こう reading, though. Just think of your junior being こういち.
あ、コイツ、オレの高校の時の後輩。
Oh, this guy is my junior from high school.
明日、会社の後輩と飲みに行く予定なんだ。
Tomorrow, I'm planning to go for drinks with my junior colleague from work.
先輩後輩の関係って、堅苦しくて好きじゃないんだよね。年、一つしか変わらないんだし、タメ語でいいよ。
I don't really like the formalities of senior-junior relationships. We're only one year apart in age, so you can speak casually.
お前は俺のお気に入りの後輩だから、どんなことがあってもちゃんと面倒みてやるよ。
I’ll take care of you, no matter what happens because you’re my favorite underclassmen.