そくおん
geminate consonant (small "tsu" in Japanese)
Noun
拗音ようおん(ゃ ゅ ょ)と促音そくおん(っ)の出だし方かたも、加くわえていただけると参考さんこうになるかもしれません。
I think it might be useful if you could add how to output the diphthongs (with small ya/yu/yo) and geminate consonants (with small tsu).