Like Katana (a.k.a. Tatsu Yamashiro), Maseo is an accomplished martial artist, and he will be introduced through flashback sequences as Oliver Queen's (Stephen Amell) handler. He would eventually grow to become his teacher and friend, playing an important role in Oliver's journey to become Arrow. Both Karl Yune and Devon Aoki will have major recurring roles, but it isn't specified how many episodes they will appear in, or when they may debut.
We reported last month that four new characters would be introduced in Season 3, two of which will be featured in flashback sequences when Oliver was on the island. Although their names are different, "Toshi" and "Akiko" from that report fit the descriptions given for both Maseo and Tatsu. The other two characters, Daniel and Seth, will be featured in present day Starling City. Daniel will be a recurring character in Season 3, described as a handsome and enigmatic entrepreneur who develops an important piece of technology. Seth is a criminal with a chemistry background, who creates a new drug that drains a person's willpower.
Karl Yune's acting credits include Real Steel, Speed Racer and Memoirs of a Geisha.