He has a few quirks that are endearing to his girlfriend.

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2p Denmark:

Magnus scrunches up his face as he does his paperwork, it is adorable and a little silly.
(Y/n) giggles after seeing this face.

He has a habit of humming while cuddling and cooking, (y/n) sometimes joins in.
He does not realize he does it until she joins in.

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2p Sweden:

Bernard has a habit of sniffing things, but the face he makes causes him to look like a giant puppy.
(y/n) can't help but smile when her boyfriend sniffs and cuddles her.

The swede also likes to stare at nothing, he will make a goofy dreamy face when he does.
He usually stares in the direction of his adorable girlfriend.

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2p Finland:

He mumbles in finnish.
It can be random sentences, or rhymes.
(y/n) finds it cute when he absent-mindedly starts to sing rhymes like a song.

He often makes cute pouty faces when tired.
His sleepy faces are the best faces ever.

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2p Norway:

He sometimes forgets where he puts things.
Loki goes around and calls out for the item like it is alive.
He usually loses his glasses, after forgetting he is wearing them.

Loki does not realize that he dances a little while he works.
He likes to listen to music as he works so It is no surprise.

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2p Iceland:

He gets shy when he loses his eyepatch.
He tends to shy away from windows afferwards.
Egil hides in his girlfriend's arms when this happens.

Egil sometimes starts to talk Icelandic when excited.
(y/n) can't understand him when he does but his cute face is worth it.