Hideo Kojima originally had "no plans" for a character like Metal Gear Solid's Cyborg Ninja until Yoji Shinkawa's art had him saying "hell yeah, a ninja cyborg!"

gamesradar.com:

Metal Gear Solid's Cyborg Ninja is one of the 1998 game's most memorable characters, backflipping all over protagonist Snake with his chiseled exoskeleton and hissing haunting musings about life. But the cerebral humanoid soldier might not have ever got the chance to stick a katana in your face if director Hideo Kojima hadn't been so enthusiastic about character designer Yoji Shinkawa's art. 

"From the very first [design] plans I drafted, Shinkawa was in there changing things on his own," Kojima told PlayStation in a recently resurfaced interview from 1998. He cited Cyborg Ninja as a product of his and Shinkawa's "push-and-pull" creative process, explaining that he originally had no plans for a totally jacked android man. 

Despite this, Shinkawa felt compelled to draw one because, as he explained to PlayStation, "it's cool." 

"I thought he would just be a normal soldier enemy," Shinkawa continued. "I had a number of different patterns in mind, and I thought I'd try drawing something cyborg-ish, and this ninja-looking guy is what came out. Once I gave him a katana, the character really came to life for me." 

"There were a lot of things added like that," Kojima said. "'Hell yeah, a ninja cyborg!'" 

In the end, Metal Gear Solid became stocked with Kojima's and Shinkawa's most wayward ideas like an overflowing costume closet. An eye patch here, some camouflage there…

The psychic antagonist Psycho Mantis, for example, would never have been glued to his recognizable, menacing gas mask if Shinkawa hadn't spontaneously added one to his design. 

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"Why a gas mask? I don't know," Kojima said. "And then Shinkawa was saying how underneath the mask he has no face. Why no face? Beats me."

"For my part, I wasn't against adding [these details]," Kojima continued. "Unexpected things like this are part of the fun."

Nobody at Konami believed in Metal Gear until Hideo Kojima showed them the exclamation point: "This is gonna