Digging up the girls' most embarrassing memories, and their reactions to finding them is delightful.
None of them managed to stay composed, even if they put up a brave front beforehand.
Rena just going "kaeru". I laughed so hard.
Translating it as just "goodbye" doesn't really get the meaning across, but I understand the desire to be blunt about it.
More accurate would be like... "I'm going home", or perhaps "I'm leaving". Or maybe she meant "we're leaving".