This arc is lame, imho. Sudden rival after a year apart, knowing about their relationships etc. All this crap like fell from the sky, without any clues in previous 40 chapters. I would get it if she was a new girl, but not when they know each other, didn't meet in previous chapters and backstory is like "here we go, this is a girl, they knew each other, didn't meet for a year, now - fight over shy boy" - I mean - waaaat?...
Hope this crap wouldn't last long - Izumi and Shikimori slow evolving but sweet relationship is what we read here for 40 chapter, not some cheap "sudden rival" bullshit out from the sky.