Russia/Siberia is a fanmade pairing for the fanmade character Siberia for Hetalia: Axis Powers, involving Ivan Braginski (Russia) and Anastasia Charkova (Siberia). This pairing is sometimes known as RusSib, a portmanteau of thier repsective names
Ivan and Anastasia grew up together and are very close and there is a very strong bond and strong feeling of trust between the two of them.
The Selling of Russia-America
When Tiana, back then known as Tatiana, was sold away to America, Ivan was incredibly depressed and Anastasia comforted him and acted as a go-between for Tiana and Ivan, as Ivan couldn't bear to 'face the daughter' he 'sold'.
The Soviet Union
When Siberia was under the control of The Soviet Union, Anastasia expressed some uneasiness but she didn't dare show it around Ivan. When Toris (Lithuanina) asked her why, she said it was because: "Ivan is too dear to me to lose. So I won't tell him how uneasy I am. After all, one must lie to the one's they love sometimes." It is unclear what kind of love Anastasia feels for Ivan, although it is most likely the kind of love she feels for Eduard (Estonia).
After Anastasia and Eduard got married, Ivan's affections for Anastasia became much less obvious but there have been some hints; such as expressing concern for her, standing close to her and holding her when Eduard isn't around. Although Anastaisa doesn't protest to these acts of affection and possibly love, she has made it clear that it would be best if Ivan kept his love fo her to himself as she doesn't want Eduard to be hurt, however, the two of them have infact admitted to themselves, and each other, that they love each other but they won't and/or can't do anything about it.