The woman, who is jailed on suspicion of illegally accessing a computer and manipulating electronic data, used his identification and password to log onto popular interactive game "Maple Story" to carry out the virtual murder in mid-May, a police official in northern Sapporo said on condition of anonymity, citing department policy.
"I was suddenly divorced, without a word of warning. That made me so angry," the official quoted her as telling investigators and admitting the allegations.
The woman had not plotted any revenge in the real world, the official said.
She has not yet been formally charged, but if convicted could face a prison term of up to five years or a fine up to $5,000.
Players in "Maple Story" raise and manipulate digital images called "avatars" that represent themselves, while engaging in relationships, social activities and fighting against monsters and other obstacles.
The woman used login information she got from the 33-year-old office worker when their characters were happily married, and killed the character. The man complained to police when he discovered that his beloved online avatar was dead.