Cute brother and sister get transported into another world, having to survive in a fantasy setting filled to the brim with dangers. None of that matters to him though, since whats most important to him is his only big sister. Anything else is secondary.

"Little Brother, we're in a different and strange place now. There are a lot of dangers so always stay by my side okay?"

"Okay!"

So what if there's a lot of scary looking things out there, I have the best sister in the whole world right here!