I know this very late but we will do it anyway xD. Also warning this might not suitable for those innocent mind so yeah.....GG :3
Starting with the most adorable couple ever Yuri and Kuro

Yuri: *work in her office*
Kuro: *open the door to her office* Yuri c-can I have a little of your time?
Yuri: honey you know I can't disagree---*jump when see Kuro in hold a pieces of chocolate in his mouth and blushing like crazy and grab him*
Kuro: Y-yuri? Huh?! *Yuri puss the chocolate inside his mouth then kiss him and try to take the chocolate back with her tongue*
Yuri: *took back the chocolate and eat it* fufu~ perhaps I should do this everyday *pervert smile* fufu~
Kuro: *Pant* *blushing*

After 10 minutes

Kuro: Yuri please *Pant* let me rest a bit *Pant* *blushing*
Yuri: oh don't worry dear we got all day fufu~ and most importantly happy valentines Kuro *give him a chocolate by kissing him*

Well the thing that they did after that is you know.....adult stuff *wink* *wink* I swear if I can draw manga I will draw this scene :3

Seulbi and Sehan the mother freaking tsundere couple of all time

Seulbi: Sehan please careful *try to puss him back from the attack and caught him off guard so she knock him down* sorry *help him to stay up
Sehan: no need to Seulbi, I gotta say you really skill with the speed battle style also it make you look very beautiful too....... *blush* I mean it not like I like you or anything...
Seulbi: *blush* S-sehan *took out a box of chocolates and give it to him also she look away when she give it to him* don't get any wrong idea I just made too much I g-give it to you...

Yeah you probably know where this is going right just like in romance anime :3

Now move Shibuya
ArtaeKo sorry using Anna Xilla and Zephyr again

Shibuya: *making Chocolate himself then wrap it beautifully* alright we done. Now we have to do is give it to her with out being see by Xilla and  Zephyr....*try to sneak in to met Anna*
Anna: *doing the house work like usual*
Shibuya: *knock at the back door with is next to Anna place*
Anna: S-shibuya? What are you doing here?
Shibuya: i-i want to give you this box of chocolates on valentines day but I sorry I late and I wanted to say that I really like you Anna
Anna: *blush a bit*......uhm thank you Shibuya *smile a bit at him* Ah-
Xilla: *appear from behind Shibuya* you don't know when to give up aren't you Shibuya?
Shibuya: I only give up when I not love Anna anymore and that is impossible for me not to love Anna.
Xilla: didn't you read the update that ArtaeKo write before? she already got a crushing someone else idiot?
Shibuya: I don't care as long as Anna haven't confirm that with him then I will still try
Xilla: *sign* you are one hard head Shibuya but don't break your heart when see her dating her real Bf.

I think that all couple I have in my Oc's a big thank to ArtaeKo for let me using her On like Anna Xilla and Zephyr Since my Oc's x Oc's chapter I know I know what took me so long to make that chapter well I'm doing a one shot for Shibuya and Anna so yeah....