The Hikari-focused apparent fanservice reminded me a lot of Nick Creamer’s commentary on the Araragi/Nadeko “playdate” scene from his article on Nisemonogatari and the nature of fanservice. In that scene, the camera isn’t leering at Nadeko so much as Nadeko is doing her best to pose for the camera. Nadeko is in control of the camera in her attempts to seduce Araragi. Based on the first episode of Seiren, it seems as though Hikari is making an effort to pose for the camera as well, especially in the scene where she approaches the study group. I think she’s using her sexuality as a means for intimidating MC-kun.