Kanon's Valentine Special Contest Last Hint!!

The last hint for the contest was already in the 4-koma manga page I posted two days ago... or maybe it wasn't. The same could be said for quite a few more pictures of Kanon you have seen before because the last hint is:

It's something you've already seen Kanon wearing.

So the real question is: When?

I think I'll take the chance to make a little chronology of Kanon's story (something I've been wanting to do for some time, so I'm taking the opportunity to do it now). Let's start with the first year of university and call that year: Year 1

YEAR 1:

March:

• Hiro receives the notice he won the scholarship at Kanon's father's university and decided to confess to Kanon.
• Kanon and Hiro graduate from High School. Hiro confesses to Kanon that day, after the ceremony and Kanon says YES.

April:

• Hiro moves out of Kanon's house.

July:

• Something BIG happens that affects the relationship between Kanon and Hiro. What happened will be revealed on Teaser~Trip~Kanon (so I can't talk about it because of spoilers).

October:

• Kanon and Hiro have sex for the first time.

December:

• Kanon begins her "agreement" with Yukihiro.

YEAR 2:

February:

• Kanon's Valentine Special chapters 1-3 take place.

March:

• Kanon's Valentine Special chapter 4 takes place (White Day chapter).

June:

• Teaser Date Kanon takes place.

July:

• Teaser~Trip~Kanon takes place.

Teaser~?????~Kanon takes place sometime between the time Kanon begins her relationship with Yukihiro and Teaser~Date~Kanon

Xmass is a spin-off/what-if scenario (at least for now), so no place in the chronology. Unless I can make it fit somehow, it's not a Canon chapter.

About the Picture in this post:

As you know, there will be two winners in this contest. One person already got the answer, but he wanted someone else to win the prize (a very nice guy). I think it's only fair he also receives a prize. So we will have two winners this time.

The picture above is a W.I.P. of the commission he requested. I'm still working on it, so not even the angles are decided yet, but I think it will be a 3-5 CG progression with a little story about Kanon sitting on Yukihiro's face. 

Anyway... I think I've given enough hints... One more and I might be just giving the answer away to the first person that sees the post. So this is the last hint.

You can check the other ones on these posts:

Hint #1 

Hint #2

And once again the question is:

What will Hiro give Kanon on White Day?

You have till the release of the final chapter of the Valentine arc to answer, so you still have time! Good luck and stay healthy!!