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.
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?
あの車、もっと本気で止めればよかった。
I should've tried harder to stop that car.
そろそろ本気モードのスイッチ入らないかな。
I wonder if it's time to switch to serious mode.