Aph East Malaysia - Tumblr Posts
*one day, Malaysia Timur decided to show the other nations a picture of her & Barat when they were younger(Borneo & Melaka)*
Italy: wow Timah! you look very pretty in here! *points at a cheerfull girl with a hibiscus in her hair*
Malaysia.T: eh? That's abang lah. *points at a serious and flustered boy that was being hugged by the other* that's me.
Other Nations: ....
Nations that have known them since their younger days: yeah, we were also fooled once...

Demon Slayer Au with Malaysia Barat as a Demon Slayer and Malaysia Timur as a Demon.
When Malaysia Barat & Timur were younger (Melaka & Borneo), their personality were different. Melaka used to be the cheerfull and happy go luck brother while Borneo was the protective and serious sister. After Japan's colonisation, the twins personality changed as if they switch personality with each other (and also the fact at one point they look very identical).
Which is also the reason, to this day, why Singapore gives confused looks to his brother and sister.