>>16125941No one thought of it at the time because Gura was only just starting her own transformation arc, so Kiara (because she was still uncontested considered to be the closest to Mori at the time) and Ame (has a reputation for support behind the scenes+/ameg/ buff) were considered the most likely candidates. However, we know that even back then Mori and Gura were close so it's not unreasonable to assume they'd be open to talking about that stuff with each other. The absolute most important thing to consider is that it just makes the most logical sense for it to have been Gura because she was the person who would have been affected by the collab in question, being the other person that was there and all. If Mori felt bad enough about it to immediately take the video down at first, there's no way she wasn't twisting herself into knots apologizing to Gura for it, which realistically would have led to the conversation.
https://streamable.com/yt9qg2