You could also try the particle for belonging の which is a bit like " 's " in English. Should appear in hiragana (as a standalone syllable) frequently since it is a particle much like the first one they suggested (ha for the theme of a sentence). The second one (su) tends to be at the end of maybe half the verbs, might be why it's less likely.
Another one which might match is Japanese punctuation, such as the comma 、 and the period 。
https://www.tofugu.com/japanese-grammar/particle-no-noun-mod...