Serious
Seriousness
noun, な adjective, の adjective
What is book energy? It is energy you put into reading - it is your studies! In order to have book energy, though, you have to be very serious.
ほんき
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.
いつになったら、本気を出すんですか。
How soon before you make a serious effort?
ついにコウイチが本気を出してきた。
Koichi is finally getting serious.
私があの男の頭の毛をむしったなんて、本気で思ってないよね？少しは私を信用してよ。
You didn’t seriously think I pulled that guy’s hair out, did you? Give me some credit.