Kana flick (Gboard) is actually pretty good, at least due to bigger keys. Also, Kana is always created, rather than mixing with alphabets on typo.
Repeated tapping to advance through the row, but I don’t know to force advancing to the next character. Hold the key always force advancing to the next character.
The speed is just the matter of getting used to, but mobile typing isn’t like desktop with keyboard, anyway.
That’s “twu”. “h” and “w” are the first guessing candidates. I have to type トゥーリ a lot nowadays.