na-adjective
monomaniac; obsessive about one thing
Describes a person or behavior obsessively focused on a single subject or idea. Often used as a な-adjective.
彼は鉄道に関してはモノマニアックだ。
He is monomaniacal when it comes to railways.
モノマニアックな趣味を持っている。
I have an obsessive hobby.