Trope Listoo
Age Appropriate Angst: The entire foundation for Isao's character stems from the death of his father and subsequent abandoning by his mother. If the cast had met him younger, his attitude on life would be tragic and probably troubling, instead of making him seem like a badass.
Anti-Hero: Specifically, of the Type III variety on the scale. A bad attitude backed with a near-limitless determination to see his goals achieved, and a complete thirst for stronger opponents. Given his tendency to far from the eyes of more moral teammates, Isao is well aware of what kind of person he is when the cards are down. So don't call him a good guy, unless you want an earful.
Badass Biker: On the biker side: Not only is Isao a motorcyclist par excellance to the point that it's a quintessential part of his character, but he also tends to be found in the classic pose, churning through half a pack a day like it was cool and handing out his own street-influenced advice. On the badass side, Isao is not only one of the most combat-experienced members of SEES, but he is known for his never-say-die attitude, his readiness to fight all day and party all night, and his strangely thick accent.
Blood Brothers: Isao and Chieko. They also double as heterosexual life partners, despite both being bisexual. Ironically subverted in that they are not a Brother Sister Team; while both were members of SEES, they only worked together on a handful of occasions.
Bruiser With A Soft Center: Sure, he looks and acts scary as can be, but it's really something of a facade. Isao not only loves kids, and absolutely detests the idea of them being hurt, but if you hurt one in front of him, he'll go out of his way to smear you across the pavement. It's not just children, too, pretty much anyone younger than him that's willing to see past the gruff exterior's going to find themselves with all the protection and advice they could ever need.. And no, even with other members of SEESIT aren't safe from this attitude. Just be very careful about hurting them, because it's a co-dependent relationship.
Dark Is Not Evil: Despite being a biker with criminal ties and the ability to summon what's historically a messenger of death, and having dropped several hints act about having actually murdered someone, having blatantly stolen a variety of cars, and blown up a building or two, Isao is actually considered a good guy by most of the cast.
Establishing Character Moment: Isao's first major establishing moment with SEES was during the Strength battle, where, having isolated the shadow to a boat with the rest of the cast, and raining Zio stones (it's weakness) down on it, Isao grabs his last one, pauses to light a cigarette on it, and rattle off a one-liner before tossing it. And that was before he was catapulted to a team leader in the Inaba plot and had to man the fuck up.