One Track Mind
Single Mindedness
noun, な adjective
You have only one book energy. No other books cross your mind. Only this one book. Why? Because you have such a one track mind.
いっぽんぎ
The reading is based off the on'yomi readings for everything, though every reading is slightly altered. いち getting shortened to いっ, ほん changing to ぽん, and き gets changed to ぎ. They're based off the readings you know already, though, so making this shift shouldn't be too hard... that is, unless you have an 一本気, ammiright?
かれは、とても一本気なせいかくです。
He has a really single-minded personality.
モテないだん子には、じゅんじょうで一本気なおとこがおおい気がする。
I feel that many men who are not popular among girls are naive and single-minded.
俺の親友は、とても一本気な男で、90歳になった今でも初恋の女を思い続けている。
My best friend has a one-track mind; he’s 90 years old and still has feelings for his first love.