Don't say it with 〜てはだめだ

Grammar Explanation: Must not do with 〜てはだめだ

Syaro gives a vague account of her first meeting Rize, as the truth is too embarassing for her. When Cocoa misunderstands the event, Rize prepares to tell what really happened.

シャロ:: 「あっ言(い)っちゃだめです！」; “Ah, don't say it!”; Literal: “Ah, it is no good if you say it!”

Key Points

1言(い)っちゃだめです tells Rize not to reveal it

Syaro tries to stop Rize from giving the embarrassing true account of their first meeting.

2言(い)っちゃ contracts 言(い)っては

The casual contraction combines with polite です, which fits Syaro’s urgent but respectful plea.

3あっ shows the interruption is immediate

Syaro reacts as Rize prepares to speak, so the line functions as “wait, don’t say it!”