I had arrived on Miyajima late in the day but I was spending the night there and got to see the island after dark. The guesthouse I stayed in was just a bit south of Itsukushima Shrine and at the bottom of Mt Misen. A small stream ran nearby and the paths through the woods led me around to the backside of some of the other guesthouses in the area.
With the exception of the local grocery store and a couple bars/restaurants, Miyajima largely shuts down for the day at around 6:00pm. The island’s main commercial area is nearly empty at night and you won’t see that many other people since most of Miyajima’s visitors are day-trippers from the mainland. While wandering around be sure to keep an eye out for the local deer. The people may mostly be gone at night but the deer still can still be seen roaming around the island.
Itsukushima Shrine’s torii gate is illuminated after the sun goes down and is worth seeing if you’re on the island at night. In 2019 when I visited the gate was covered for restoration work but hopefully by the time Japan reopens for tourism it will be uncovered again.
The shrine itself is partially lit at night but is only open during the daytime. Normally the shrine is packed with visitors so passing by it at night when everything is quiet is a nice experience.