Well we honestly will never know! Apart from the one necklace that we know FSF gave YM for her birthday once, all the others we have zero clue about...despite the fact that FSF revealed he buys her tons of presents. Haha. And I'm sure YM must return the favour...actually this is COMPLETE speculation so don't take it seriously at all. But I have seen some fans speculate this one shirt that FSF wore was given to him by YM...because the brand is one that she apparently buys a lot of, and it's some cutesy Japanese clothing brand that a 30-something man is unlikely to buy. LOL. Again complete speculation and could very well have been a gift from someone else (or maybe he just saw the shirt and really liked it).
Well we do know YM gives/lends him lots of books! (Even assigning him "homework" and checking up on him the next time they meet up to make sure he actually read it. Seriously--she apparently makes him take notes while reading it! )