Hello brodhar from anodhar modhar. Many adventurers asked this question before you and many more will ask it time and time again. Joking aside, the answer is never changing and always stays the same:
You
can't improve yarizo relationship to level 4 by any normal means throughout the whole game... Yet. Blame it all on technobrake's idea of porting the game to another engine instead of making new content for the fanbase.
Don't fret, there is another way to access a little bit of diversity regarding existing scenes. All you need to do is to use Portable cheat item and activate "Event test mode", if you didn't do so already.