i know swiftkey, its installed by default on my sony xperia, but i use google GBoard.
there is also an japanese keyboard available.
i just startet learning japanese 5 days ago, so i didn’t use this but i’m not sure,
what do you mean by “do not lern romaji”
i disabled the menu option in Drops, because i couldn’t concentrate on reading the kana because it’s much easier to read romaji and choose the correct picture
i think you must “use” romaji for writing. i also use the app Scripts and for “offline learning” i write the romaji on a page in my notebook and then practice the writing of japanese signs on that page
i couldn’t imagine a way to connect the sound of a sign without writing it down in romaji