hanamaru
Silent i and u
An i or u between two hard consonants, and the final u of です and ます, is whispered: “des”, “mas”, “s’ki”.
Japanese sometimes drops an i or a u almost entirely. It happens next to seven consonants: k, s, sh, t, ch, h and p. What the seven have in common: put a finger on your throat and say a long “sss” — nothing buzzes. Now say a long “mmm” — it buzzes. All seven are the sss kind, made without the voice. When a short i or u lands between two of them, or last in a word after one, Japanese simply does not switch the voice on for that vowel. The mouth shapes it, but it is whispered.
You hear it all the time. です sounds like “des” and ます like “mas” — the final u disappears. すき is “s’ki”, not “su-ki”. And in よろしくおねがいします the i in し is whispered: “yorosh’ku”. It is why Japanese sounds faster than it is — some vowels take almost no time.
You do not need the rule to speak correctly. Listen to the words and say them back and it comes on its own. But when you wonder where a u went: it is still there, only silent.