The more common (and according to my little research) pronunciation of this Kanji is "Ken". There is Kata, but not Katashi, and all people named with this Kanji I've seen are named "Ken".
I am planning to use this name for a character in a story I'm writing, I was literally randomly generating names for this and this was the first one and I think it fits him well.
― Anonymous User 2/20/2021
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Katashi Ishizuka is a Japanese voice actor who is affiliated with Aksent.
Ishizuka Katashi(石塚堅) is a voice actor. Notable voice role was Ryu in Street Fighter.The kanji 硬 could also be used; Oyama Katashi (小山硬) is a Nihonga style (or Japanese-style) painter.
I have never heard this name in Japan. Takashi is common, not Katashi. Besides, Ken is a more common pronunciation for the Chinese character (Kanji) shown in this name.