>>7671438I have a few siblings, and I do agree that kids can be annoying. But if you've been a big brother long enough, you kinda develop a paternal instinct over them. You start to gloss over the annoying part after a while, because all you'd want to do is make them happy and be a good role model. It's nice to have someone look up to you, someone that will think you're cool no matter what skills you possess. Whether you're a gaming god, a great artist, a super athlete, or even a super smart nerd, they'll aspire to be like you because they love you so much. Even if you end up a NEET, they'll still love you because they know even big brothers go through hard times. All of that pays off when you get to see your little sister smile and laugh. It fills you with a warmth that you can't really get any where else (except if you watch Lily of course.)
tldr: little sisters are cute, seeing them laugh & smile warms your heart, and it feels great knowing they'll always love you.
Lily hits all these factors so perfectly and that's why we all love her so, so much!