Translation guide
In Japanese, expressing obsession depends on the nuance: being mentally consumed by something, being a passionate fan, or being fixated on a person. The most common and natural expressions are 〜に夢中 (muchuu) for being absorbed in an activity or hobby, and 〜にハマっている (hamatte iru) for being hooked on something. For romantic or creepy obsession, different terms apply.
To be so into something that you can't think about anything else; to be hooked or addicted to a pastime.
Means 'to be absorbed in, crazy about'. Very common for hobbies, games, or activities. Can be used positively.
彼は最近ゲームに夢中だ。
He's been obsessed with games lately.
Casual, very common. Means 'to be hooked on, addicted to'. Often used for hobbies, TV shows, or collecting things.
最近、韓国ドラマにハマっている。
I've been obsessed with Korean dramas lately.
More formal/literary. Means 'to be immersed in, to devote oneself to'. Often used for work, study, or serious pursuits.
彼女は研究に没頭している。
She is obsessed with her research.
Means 'to be into something as a hobby, to be particular about'. Often used for crafts, cooking, or collecting. Can imply a deep, sometimes eccentric interest.
父は盆栽に凝っている。
My father is obsessed with bonsai.
To be unable to stop thinking about someone, often with a negative or unhealthy connotation.
Means 'to be attached to, to cling to'. Often used for unhealthy obsession with a person, ex-partner, or idea. Can be negative.
彼は元カノに執着している。
He is obsessed with his ex-girlfriend.
Loanword for 'stalker'. Used to describe someone who obsessively follows or harasses another person.
彼女はストーカーに悩まされている。
She is being harassed by an obsessed stalker.
Literally 'can't think of anything but ~'. Expresses being completely preoccupied with someone, often romantically.
彼女は彼のことしか考えられない。
She is obsessed with him; she can't think of anything else.
To be unable to stop thinking about a particular thought, fear, or concept.
Literally 'to be possessed by'. Used for being haunted by an idea, fear, or obsession. Strong, often negative nuance.
彼は死の恐怖に取り憑かれている。
He is obsessed with the fear of death.
Means 'can't get ~ out of my head'. Used for persistent thoughts, worries, or catchy tunes.
その曲が頭から離れない。
I'm obsessed with that song; I can't get it out of my head.
Both mean 'obsessed' in a positive, hobby sense. 夢中 is slightly more formal and can be used in writing. ハマっている is very casual and conversational. ハマっている often implies a recent, addictive interest, while 夢中 can be longer-lasting.
彼は歴史に夢中だ。
He is absorbed in history.
彼は最近ポケモンにハマっている。
He's been hooked on Pokémon lately.
The English 'obsessed' covers both positive enthusiasm and unhealthy fixation. In Japanese, using 執着 (shuuchaku) for a hobby sounds overly dramatic and negative. Use 夢中 or ハマっている for positive contexts.