I think I've done most of everything else but I still don't know what the vertical thing is about. Also can anyone tell me what the fifth costume is in Suzune's notes?
Not gonna lie, I completely forgot about that character... But I can tell you that I 100%'d everything without ever using her "hint", so it's probably not important.
The hint in Japanese is 縦 (Tate), which can also mean Shield... maybe she is telling Sakura that she should include a shield in her style that uses 5 weapons? I think it's just banter, not a real hint.
As for Weeping Cherry, I believe you have to WIN the heartache battle, which is essentially a superboss. You can also acquire it via the Development Room after beating the extra chapter (The Development Room can be accessed in the Gallery at the bottom right).