During the Dark Hour on the sixth full moon (September 5th), the team is the lounge with Fuuka searching for the expected shadow. While she is still searching the team is wondering where Junpei is, Chidori takes over Fuuka's body and tells SEES not to challenge the shadow that night.
The team goes to Paulownia Mall after the ordeal, and Fuuka begins scanning the place and finds the shadow in the wiring room of Club Escapade, after Shinjiro remembers that Rise Kujikawa's gig in the club was cancelled due to a malfunctioning power supply. The team heads out to confront and successfully defeat it.
The Arcana Hermit uses electrical skills, due to being hooked up to Club Escapade's wiring. It mainly relies on Zio-type spells, sometimes backed by a Mind Charge, so keeping Elec-weak partners and Personas away is advisable. Its signature move, Giga Spark, requires three turns to charge, so it's best to hammer it on the first two turns and switch to defensive (and hopefully Elec-proof) Personas for the big hit.
The Hermit Arcana represents a person who is introspective, reclusive, seeks philosophical searches, and understands one's self. The dark side of the arcana is a person is unable to keep to oneself, has complete disregard and no respect for society and is inhumane. The latter can be seen in how the Arcana Hermit drains the energy of the mall (and perhaps the city in time) to increase its own power. It may also be reflected in its unnaturally long charge time for its Giga Spark attack, signifying that it does not realize its great vulnerability during this time.
In Persona 4, during the team's visit to Club Escapade, Rise mentioned a gig she went to at the club, was canceled due to a power failure. In Persona 3, Shinjiro mentions hearing the owner of Club Escapade complaining about the power outage and how he had to cancel "some big event", which suggests this might have been what had canceled Rise's gig.