Flick input - an input method commonly used with smartphones in Japan - allows you to flick a character in a direction to quickly type kana. Just tapping instead of flicking gives you a kana with the 'a' vowel. Tapping the same character more than once iterates through the vowels, in a loop. How do you type the same 'a' vowel character twice?
E.g. ああ, かか, ささ
The way I've been doing it, for as long as I can remember, is to tap the character once, add a space, a backspace and then type it again. I'm hoping there is a more elegant solution.