The name Tokiya is written トキヤ which would imply it's of foreign origin but I'm not having any luck uncovering the origin or meaning of the name. It seems to be somewhat traditional. Ideas?
Maybe you mean this character (キャラ) :
一ノ瀬トキヤとは、PSP専用ソフト「うたの☆プリンスさまっ♪」および テレビアニメ「うたの☆プリンスさまっ♪ マジLOVE1000％」の登場キャラクターである。
The same deal with タツヤ. -- 達也 used to be a common name, but the 也 looks too old-fashioned now. So it's often written in Katakana.
Jp names (esp. of comedians) are often written in Katakana just for the interesting look (visual impact) -- like the weird spellings like Cyndi and Krysti ....
Also, トキヤ is a very uncommon name. Maybe the creator wants the fans to keep guessing how it'd be written in Kanji.