
"lemon" in a book title means it contains hardcore imagery. Since that is more of a stolen word than a misused one I guess this isn't technically Engrish, but it fits here.
I am afraid to translate the japanese on this book but I will, for the sake of you, the reader.
小池真理子 means:
小 small
池 pond
真 true
理 logic
子 child
-- it is the author's name and I don't feel like figuring out the reading. What, were you hoping it would be juicy?
もっとも純粋で
もっと more
純 pure
粋 refined
純粋 = junsui, genuine/pure
もっとも不安な愛
不 un-, opposite of
安 peaceful
不安 - fuan, uneasiness/anxiety
愛 love
Um... so the pink thingy says 'more genuine, more uncomfortable romance' basically. and here I was hoping that the word incest was a mistranslation. Move over V.C. Andrews, 小池真理子 has your number.
the bigger letters say something to the effect of 'romance novel fair'. Nothing special.

Comments
Er...
Lemon?
Slang
I don't write the slang, I just fumblingly translate it.