
I think the other reply already explained it but if you check the raw, probably they only refer it as liking or admiring someone, cause the word "tsuki" can actually mean liking as in admiration, friendly, familial way not only romantically...
Like when you said something like "I really really really love you mom/dad" or something similar to that ヾ(❀╹◡╹)ノ~ cause in some countries they probably love to brag about their siblings' achievement or looks, in korea and japan i think there's even a specific word for that kind of "bragging" like you're showing off how cool your siblings are but you're too shy to admit that they're cool to they themselves.. sometimes it's also for their ego booster too LOL "look how cool my siblings are ٩(๑❛ᴗ❛๑)۶"
Why tf is it so normal for little siblings to crush on their older siblings in manga?? Wtf is going on over there (Japan)?????