My favorite June MC would have to be the G Blade from 2006.
There have been plenty of technically better ones, but being a die-hard Kingdom Hearts fan, I flipped out when the G Blade was released - especially so considering KH2 was released just a few months prior and I was on an extreme high that whole year from that one game. It was my absolute favorite item for a long time. June also happens to be the month of my birthday, so my friends bought me two Thank You letters as gifts c:
And while fandom-replica items like the ninja headband had been previously released, I consider the G Blade to be the real starting point of Gaia's future expansion of releasing cosplay items, which was also very exciting to think about at the time. Premium items based, loosely or no, on video games and anime and the like continue to be some of my favorites.