For those who haven't followed the division Calleros fought in Japan in February 2017, losing to Tatsuya Fukuhara for the then vacant WBO title. In his first defense Fukuhara lost the title to Yamanaka. Interestingly both of those fights were razor thin action bouts, and Fukuhara later went on to prove he was world class with a fantastic losing performance to WBC champion Wanheng Menayothin.
Since losing the Fukuhara just over a year ago the 28 year old Calleros has been busy with 3 fights, all wins. These haven't been against the best fighters but they have included a win against former world champion Mario Rodriguez.
For those who haven't seen Calleros he's an ultra aggressive, come forward fighter with a high work rate, a very exciting style and someone who will be a handful for pretty much anyone at 105lbs. He's not the biggest puncher, but has under-rated power, which combined with his volume does make him very dangerous. At 28 he's coming into his prime, he's fairly big fighter for a Minimumweight and has fought at Flyweight a number of times.
At the lower weights competition for contenders to face on their way up can be a bit thin. Calleros however has faced good fighters through his career. This has included a narrow loss to Julian Yedras, 12 round decision loss to Francisco Rodriguez Jr, a win over Carlos Perez, the loss to Fukuhara and the aforementioned win over Mario Rodriguez. He might not be in the top 10 of the division, but he's certainly not too far outside of that group.
As mentioned Fukuhara lost the title to Yamanaka in his first defense, last August. Since the the 22 year old champion hasn't fought, but has clearly been preparing hard for his first defence and to continue his 8 fight winning run.
The Japanese youngster made his professional debut at the age of 17 and struggled at times early in, going 7-2, with an opening round loss to Kenta Shimizu in his 5th bout and an upset loss to Roque Lauro in 2014. Since that loss to Lauro however we're see Yamanaka his his stride with notable wins against Takahiro Murai, Ronelle Ferreras, Merlito Sabillo and Tatsuya Fukuhara. Like the challenger he's a busy fighter, who will throw a lot of punches. Technically he's a bit limited, but with his youthful energy he's got good stamina, beating Fukuhara at his own game, good speed and an under-rated boxing brain.
Sadly Yamanaka does lack fire power. He's only scored 4 stoppages in 18 bouts, and only 2 in his last 11 bouts, with the last two of those coming against terrible Thai visitors. His lack of power will be an issue at world level, and whilst he has got the energy, speed and skills to hold the title for a bit against the right types of opponents, though against someone like Hiroto Kyoguchi he would likely be ripped apart due to the significant differences in power and physical strength.
Coming in to this one we're expecting a really thrilling bout. Sadly though we feel that the maturity and physical strength of Calleros will be the difference. The two will have an insane action bout, but the challenger will be too strong for the champion, who is one of the sports youngest current champions and will obviously be able to come again in the future, with a bit more experience and physical development.