According to one of our most reliable source it seems almost certain that that vacancy will be filled with a bout later this year between the #1 and #2 ranked Japanese Flyweight contenders. They are former champion Takuya Kogawa (23-4, 13) and Hiroki Saito (9-4, 5).
At the moment the current rankings don't show Kogawa and Saito as the top ranked contenders though they will be when the rankings are updated over the next few days and a bout between the two is set to be publicly announced.
On paper the bout isn't the most attractive contest possible. It looks like a bit of a mismatch in favour of Kogawa who is a fringe world class fighter, though a win for him could open the doors to a lot of exciting match ups such as a rematches between Kogawa and Muranaka or Kogawa and Hayashi. For Saito however this is a great opportunity and a great chance to continue his current run of good form, which has included a very notable win over Jo Tanooka.
This match up explains why Kogawa has been removed from the May 2nd Dangan card, Dangan 127, on which he was supposed to fight Hayato Kimura. It's a shame we're not getting Kogawa Vs Kimura but it's great to see Kogawa getting a chance to reclaim his old title.
Hayato Kimura faces late replacement as Jomar Fajardo replaces Takuya Kogawa
Japanese Flyweight title remains vacant as Muranaka overcomes Hayashi