Hii! Thank you so much, I'm glad you're enjoying the game!
Here are some hints to help you unlock those endings for Xiao:
Ending 1 – At the very beginning, open the laptop and look at the chat with Lumine (this option is available if you've completed at least one ending of the Feb 14th story). Go to meet her at the cafe and agree to her adventure: "Go on a little trip with Lumine".
Ending 9 – To unlock this one, you must first complete Kazuha's April 1st Ending 3 – "No time for jokes". When Xiao is waiting for you at home, a new option will appear: "Watch TV with some chips.".
Ending 11 (Secret) – This is a massive crossover ending! First, make sure you have fully unlocked Xiao's wedding finale (Ending 10). After that, play Lumine's route. When you are at the hotel at night, choose to escape from her (grab the card and run). Xiao will catch you in the dark alley and take you back home. Lumine was just a temporary harbor... ;)
Good luck with finding them! Let me know if you need anything else!