i am an older sister too and do act like a second mother to my brother sometimes lol but there is a limit, esp about his own personal relationships. it cringes me to see a sister being that protective over her university age sibling. being THAT possessive over a sibling looks so weird. reminds me of those weird "boy moms" who gets jealous over their sons. like ew why are you going cuckoo bananas over the thought of your sibling kissing
i get that there is already an childlike innocence to teerak and conflicts in the shows are ridicilous bc its a comedy but i guess this behaviour is exceeds my cringe limit. its too infantilizing, i cant find the humour in it. i hope to see it lessens in future eps
ALSO i feel like its was not written as a character trait but just as a plot device to create conflict. so it makes even more annoying to watch and cant really warm up to the character.