Both had non-life-threatening injuries.
Police said they arrested a 30-year-old suspect for allegedly stabbing a 44-year-old man in the chest on Sunday with what appeared to be a kitchen knife.
The suspect also allegedly stabbed a 27-year-old woman in the back before he fled, media reports said.
Police said they are investigating the case as possible attempted murder but declined to give further details.
They also did not comment on the second reported stabbing.
Kyodo News and other media said the injured man, who worked for the HKT48 theatre inside the complex, saw the suspect in an unauthorised area and told him to leave.
The suspect was a regular at HKT48's fan events, Kyodo said, quoting police.
HKT48 said in a statement that the staffer was recovering at a hospital.
Police said they were also investigating a separate stabbing on Monday in another part of the city but declined to give details.
An older man was stabbed by a younger man on a sidewalk near a main train station, according to media reports that said his injury was apparently not life-threatening.
Violent crimes are rare in Japan, which has strict gun control laws.
But in recent years there have been a number of high-profile knife attacks.
