Of the two men it's been Naito who has been on our radar the longest. In 2014 he became the Japanese champion at 130lbs, stopping Hiroyasu Matsuzaki, and at the time it seemed like the then 22 year old was on his way to huge success. His title reign would see him successfully defending the title against talented fighters, like Kento Mastushita, Shingo Eto and most notably Masayuki Ito. He would also score a win at Lightweight against Nihito Arakawa.
In late 2015 Naito's reign came to an end, as he was beaten by Kenichi Ogawa and since then his career hasn't really gotten going again. He scored a clear win over Chaiyong Sithsaithong, struggled past Argie Toquero and then suffered a second loss to Kenichi Ogawa. He seemed to put that loss down to making weight and has since dipped his toes at Lightweight before finally moving up to Light Welterweight, where he scored a notable split decision win over China's Baishanbo Nasiyiwula.
At his best Naito is a talented boxer-mover. At times he's ignored his strengths to fight as a brawler, and he can hold his own at brawling, but does lack some of the physicality that he may need to make a real mark at 140lbs. He doesn't hard, and has scored just 2 stoppages in his last 15 fights! When he boxes however he can look very good, as he did when he comfortably out boxed Nihito Arakawa and Chaiyong Sitsaithong.
Filipino fighter Arienza has been a professional since 2008 and went 9-0-1 to begin his career. Sadly though he would then suffer back to back losses, including one to future Naito opponent Masayuki Ito. A short run of stoppages was then ended back back to back losses to Daishi Nagata and Dante Jardon. Another small run of wins followed before he losses in a WBO Asia Pacific title bout to Akihiro Kondo and since then he has gone 1-1 with the loss coming to Foley.
Interestingly coming in to this bout Arienza has gone 0-3 in Japan, 0-5 outside of the Philippines. He's a decent fighter on the domestic level, but the reality is that his record is a very padded one with very few wins of any real worth. That's not to say he couldn't score a decent win, but he hasn't yet, and in fact he's often shown to be relatively easy to out box. He has struggled to even win rounds against the likes of Ito and Kondo and despite pushing Nagata hard it was just Nagata's 2nd bout at the time.
There are much better 140lb fighters in both Japan and the Philippines than these two. Out of these two however it's hard to see anything but a clear win for Naito, who should be able to take either a very wide decision or a late stoppage to claim the title. Unfortunately for Naito however a win here will put a huge bullseye on his back for fighters like Koki Inoue, who are going to be actively chasing titles through the rest of the year.