Yoshimasa is a slim man who seems to be of average height. He has short, dark hair which is styled to the right and dark coloured eyes as well. He wears black quadrangular glasses too. Yoshimasa is said to have a baby face and he even described himself as "cute".
Yoshimasa was an extremely cheerful and kind person. He liked to joke around a lot and tease others around him. He is described as sociable and bright, but also very noisy by Shamrock. He also says that Yoshimasa laughed a lot and was liked by everyone around him. Yoshimasa was shown to love and care for his family a lot.
He was part of a unit, which also included Toma, Shamrock and other C3 members, that had the mission to capture Tsubaki. However, Tsubaki was much stronger than any of them and their mission failed. In the end they needed to retreat with as little damage as possible, but it was difficult for them. Yoshimasa decided to leave the battlefield with the others as Shamrock was at the front line, betraying his best friend and leaving him as a decoy for escape. This lead to Shamrock killing himself right then and there, becoming Tsubaki's subclass and him deciding to take revenge on Yoshimasa.
An unknown amount of time later, Shamrock and Higan were involved in a fight with C3 members, Tsurugi and Yoshimasa being the only ones remaining. Yoshimasa tries to protect Tsurugi and tells him to run away to a nearby support unit. Shamrock asks him if that is Syuhei as Tsurugi and Syuhei are of similar age. Tsurugi tries to lie, but Yoshimasa immediately stops him and confirms that that is not his son. Shamrock sarcastically questions Yoshimasa if his righteousness is why he betrayed him on that day right before he attacks.
Yoshimasa manages to push Tsurugi out of the way before getting impaled and ultimately killed by Shamrock.
Hawkeye: Just like son, he has the ability to see everything within a 10km radius from a bird's eye perspective. He used it in the fight against Shamrock and Higan to tell Tsurugi where he should go.
Yoshimasa and Shamrock were best friends when they were both still working for C3 and on the same team together. Shamrock stated that Yoshimasa was the one who reached out to him back then. While Shamrock was always reserved and a bit cold, Yoshimasa was definitely the more outgoing one. They'd tease each other a lot. Yoshimasa is seen to regret leaving Shamrock behind on the battlefield a lot, stating he wants to see Shamrock again. Shamrock admits how much he wanted to be like Yoshimasa and is also shown to deeply regret what he did to him, wishing to see him one more time as well while crying. He's even willing to die as a way to pay for what he's done to Yoshimasa.
Yoshimasa was a guiding figure for Tsurugi and took care of him a lot. He was shown to care a lot about Tsurugi and treated him like his own family. During his last battle he was trying to protect Tsurugi before anything else and pushed him out of attack range right before he died. Tsurugi was horrified when he saw Yoshimasa getting killed, yelling out for him and trying to help him, but he was stopped by Higan. He begged for Shamrock to stop.
Like stated, Yoshimasa loved his family a lot and seemed to have a very good relationship with his son. Syuhei loved his father just as much, being absolutely devastated after he died. Since the day of Yoshimasa's funeral when he was still a kid, he swore to take revenge on the vampire who killed his father. Syuhei has always hated being compared to his father and even dyed his hair to look different from him, however, after his fight against Shamrock he changed it back to his original colour and doesn't seem to mind it anymore.
- "It's Syuhei. Tsuyuki Syuhei. On top of being clever like my wife, he's cute like me, don'cha think?" (To Shamrock about Syuhei)
- "It can't be helped Syuhei... dad's super strong! Everyone's counting on me!"
- "Right now, we need strong fighters in our branch! I'm counting on you, • • • !" (To Shamrock)
- "I'm Tsuyuki Yoshimasa. Pleased to meet you, • • • " (To Shamrock.)
- His blood is said to have the same taste as his son's
- He told Shamrock his son's name many times
- Shortly before dying, he left a voice mail for his wife, promising to bring home many souvenirs