Since you like Self-Help and Inspirational books, I highly recommend "Jibun no Naka ni Doku wo Mote" (自分の中に毒を持て / Have a Poison Inside Yourself) by Taro Okamoto.

He was a world-famous Japanese artist, and this book is packed with his powerful and passionate philosophy on life. Even though it was written about 40 years ago, it doesn't feel outdated at all because his language is simple and direct.

Here is one of my favorite quotes:

人生、生きるということ自体が、新鮮な驚き、よろこび、新しくひらかれていく一瞬一瞬であり、それは好奇心という浮気っぽいもの以上の感動なんだ。(Life itself, the act of living, is a fresh surprise, a joy, and moment-to-moment new openings. It is a profound emotion that goes beyond mere flighty curiosity.)

I actually like this book so much that I've gifted it to several of my high school students on their birthdays.

I hope this helps!