In which case, you might assume he was a vintage console collector. You might also take him for an enthusiast with a portable gaming device more than 20 years old.
Either way, you'd be dead wrong. Umahara, aka Bokusatsu Shoujo Koubou, or Brutal Shock Killer (BSK), is a " chiptune" or "8-bit" musician. The first is short for "processor chips" plus "song tunes", the second for the number of bits on classic gaming consoles.
He uses old gaming consoles to create digital music. He inserts a modified game cartridge into a console, which allows him to manipulate sounds, create loops and record tracks. By adding external devices - like a mixer, audio interface, speakers, two gaming devices and a computer - chiptune artists become digital DJs. Cue an adoring crowd.
Theoretically, any console can be modified to produce chiptunes. But Umahara's instrument of choice is the Game Boy.
"It has the most basic functions for making sounds," Umahara explained through a translator, before his rehearsal for the Small Theatre Big Drama Asia forum in Hong Kong last weekend. "With a PSP [PlayStation Portable], you will have more functions to make different sounds. It will be almost like someone playing a live piano or guitar. The Game Boy has limited functions and that's the fun part of it."
When he's not at clubs or performing with theatre troupes, he's pounding away on his Game Boy. Everywhere he goes, he takes his beloved instrument with him.
With his console, a modified cartridge and headphones, Umahara can create music on the go. And he does just that.
"Sometimes he can hear me, sometimes he cannot," joked Muhosha theatre troupe producer Misato Yamada, referring to Umahara's penchant for immersing himself in composing music. "He's always making music on the subway. He always carries this [Game Boy] around. Whenever he has time, he's making music."
Late last month, Umahara released a solo album, Bokusatsu Shoujos Kingdom. The title, he says, means "a kingdom of girls so cute they can kill you".
But the Japanese characters can also be read as "a factory for killing girls", which he insists is "not the meaning".
He describes the album as a mix of different types of sounds. "Overall it's very aggressive yet happy and hardcore," he says.
"It's very much an authentic video game sound."
His creativity is on full display on the record, which at times sounds like hardcore chipmunk techno.
The rapid rate of technological progress has made many consumer gadgets and electronics obsolete. But it has also created a retro niche market for chiptune artists to resurrect the old gadgets for a whole new function. Their work is testament to the saying that "one man's junk is another man's treasure".
Just ask Umahara. For him, a Game Boy is no old toy. It's a device for funky new music.