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.
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.
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.
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.
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.
He is obsessed with his ex-girlfriend.
Loanword for 'stalker'. Used to describe someone who obsessively follows or harasses another person.
Literally 'can't think of anything but ~'. Expresses being completely preoccupied with someone, often romantically.
To be unable to stop thinking about a particular thought, fear, or concept.
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.
He is absorbed in history.
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.
She is being harassed by an obsessed stalker.
She is obsessed with him; she can't think of anything else.
I'm obsessed with that song; I can't get it out of my head.