I'd say that it's definitely a good idea to split hiragana subs off into a child kit. Although, if I were you, I'd drop them entirely, or replace them with
Cangjie or
Zhuyin sublegends.
I've been playing Hitman games my whole life, and throughout all of the old-school games, Agent 47 has had a much stronger association with China / Hong Kong than to Japan. It's only really in the Hokkaido mission in the 2016 game, and a short sequence in
Silent Assassin, that he's had any ties with Japan or that the game's plot took place in Japan. On the other hand, the Hong Kong missions in
Codename 47 and
Contracts are some of the most memorable for a lot of long-time Hitman players (and definitely some of the most atmospheric). They also played into the series' lore a whole lot. The
artwork in the OP instantly reminded me of those missions, despite the anatopistic Japanese lettering. Even the ending cinematic of
Blood Money (objectively the best Hitman game *wink*) shows Agent 47 entering a
brothel parlor behind a red curtain somewhere in China.
So, either Zhuyin/Cangjie, or no sublegends at all, is the way to go in my opinion.