ok ok ok, im sick of all these guides on the internet giving long and erroneous instructions that just arent necessary.
easy fail proof method right here.
1) get to the point in the game where you are going to find ren, on the 1st of march or before.
(at this point, you can do the photo scene if you wish behind the temple to get her to call you ryo if you wish to skip #4 or you can do both)
2) go to pigeon park, talk to eileen.
3) the next morning before 1, go to man mo bistro, chat with eileen and fangmei.
4) walk back into the bistro and do the qte where you save fangmei. she should call you ryo, regardless of how much you have spoken to her.
(you can speak with eileen to get her to tell you about her bday after first talking to them at the bistro, but its not necessary)
5) go to the complete clothier, wait for fangmei, she leaves the bistro at 1. trigger the scene, walk in and buy the pendent for her.
6) go to xiuyings room on the 3rd, scene is triggered.
there are many ways to make this happen, but i find this to be the quickest, most pain free way.
the only requirements are: getting fangmei to call you ryo, meeting eileen, meeting them both at the bistro, scene at clothier / buying pendant, going to xiuyings room on the 3rd.
very very simple.