Koseki has been the Queen of the Atomweight division since winning the WBC crown back in 2008 and has made a very impressive 17 defenses, including wins over current WBO champion Ikeyama, top contender Saemi Hanagata and thtthen WBA chamion Ayaka Miyao. In total she has racked up a very impressive 17 defenses, but her competition has been criticised due to the limited talent at 102lbs. By moving up she is looking for a real challenge, and should find one in Kuroki.
As for the defending champion she is she is hunting her 6th defenses of the title that she won in late 2014. Her record might not suggest anything special but she's won her last 8 and is on a great role with wins over Mari Ando, Katia Gutierrez, Masae Akitaya and Nancy Franco. If she could add a win over Koseki she would massively enhance her record and reputation.
The bout is set to take place at the Korakuen Hall, but it's unfortunately not taking place until December 17th, giving both women a lot of time to prepare for what is likely to be a really exciting contest.