You're welcome! I'm glad that I could be of help.
Also, I just want to say that I'm really enjoying your game so far! Keep up the good work~
I tried to get this flag by talking to the younger brother and selecting "a present from your brother," but it failed to trigger the hospital scene. I can see in the code that it's written as $shuuki_story.append("91b") whereas the one with the older brother is $shuuki_story.append("91"). My guess would be that the logic in Chapter 5 is not recognizing "91b" as a valid instance of "91" because they were defined as 2 different story events.
I haven't done Chiaki's ending, but I looked in the game code to see what the conditions are. Note: in cases where I don't specify the name of the memento, it's because I haven't obtained it in-game myself. The game code only specifies the index, not the name.
To get Shuuki to keep his promise to Chiaki, you must fulfill at least 3 of the following:
Scorpio, are you still having problems triggering Yukinari's ending? I also had difficulty and ended up having to dig into the game code to figure out the necessary flags. There are some very specific choices you have to make, and it's easy to make a mistake.
If you are still having problems with Yukinari's ending, tell me:
a) Does he show up in the hospital in Chapter 5? If he doesn't you missed the flag in Chapter 4 where you visit the mansion and tell Yukinari's older brother that you are dating Yukinari. In order to get this option you must hide from the younger brother first.
b) REQUIREMENT: Yukinari must have visited you in the hospital in Chapter 5. What does Shuuki say after the time reset in Chapter 5? If he says something about it being better that Yukinari forgot, then you did not have enough affection to get the good end with Yukinari.
There are certain mementos you have to view in "active" mode and certain choices you have to make to get affection points with Yukinari. Let me know if this is where you are having problems, and I will post the list of qualifying mementos/choices to get Yukinari affection points.