TL;DR : Achivement system in this game is broken, you can't get more than half of them.

The game isn't finish and has been abandonned and the 3/4 of achivement are broken / doesn't work. For exemple, every "affinity" achievement require to perform and progress through the story... too bad the story was deleted from the game years ago. You can check my profile to see witch achivement are still obtainable (except for "event").

I won't be without my 100% even if I have to meet these developers in person

I don't think it's right to remove existing achievements, but you should go back and make the other achievements accessible in another way.

how to place the gifts that are being sold in the store and then deliver them to these characters