I've been thinking about Zhanna and Heavy's relationship alot, it's a shame we didn't get to see much of them in canon. I do wonder how their relationship was like when they were younger though... I like to think when Zhanna was born, and since I feel like she's the second oldest, Heavy was initially grossed out by her because "Eww babies, they drool and cry and pee all over the place", and also probably felt a little jealousy since his parents were now focusing their energy on their new baby, like how a lot of kids felt when they gain a new baby sibling. But then he quickly warmed up to her and became the pretty good older brother we know now! I like to headcanon that he thought her how to fight and also gave her secondhand items like toys and clothes and stuff. Man, I need more content of Heavy's baby sisters...