What was that?

I think that was the box with the incriminating letters that Isis sent to Mielle

I thought it might be the box where Aria kept the Hourglass, but that wouldn't make sense, so I was confused.

Thanks. ٩(๑❛ᴗ❛๑)۶

I thought the same at first but after looking more closely the box has the Frederick house rose on it and the next chapter starts with Isis getting blackmailed so that's why I think it's got those letters ʕ·ᴥ·ʔ