A Japanese ball-jointed doll made out of vinyl.
A lot of BJD-fans buy them as a substitute of those beautiful resin dolls when they don't have the will to work to afford one; and Obitsu-dolls are often frowned upon in the BJD-community.
"I've been waiting soooo long for my Doll-Zone Yue to get home, and guess what was waiting me when I got home from work yesterday? The package!"
"Ohh, cool, he's pretty. I got an Obitsu, we should totally do a photoshoot together!"
"... Obitsu '>_>"
Obitsu is, in reality, a type of ball-jointed doll (BJD) by the company Parabox. They are usually sold as individual parts. These parts can be used to make a doll, or, more commonly, are used to replace doll parts on existing collector dolls (either as customization or for repair).
In a more slang sense, the word is often used as a verb. To "obitsu" a doll is to replace one or more of the body parts of an existing company-made doll with Obitsu items.
"I don't like the joints on my new BJD doll, so I'm gonna obitsu it."