As Izumi's little sister you have and always will be his main concern outside of idol work. You are quite literally his whole world and he cherishes you deeply.
Izumi is extremely protective of you, he can and will (spy) keep an eye on you while you are out with your friends or even on *GASP* a date with a boy. Hand holding is strictly forbidden- to a degree.
He make sure that you come first no matter what. Practice? Not today! If you need him he is dropping it and running to you.
He loves to tease you for the silliest of reasons. Bed hair looking crazy? Oh he will tease you for it and how cute your sleepy face is.
Not feeling well? Is it- ahem- that time of the month? Fear not, he will match to the store immediately and buy you all that you need and some extra sweets just for you.
If someone is bullying you he will happily punch them, he may be a knightly idol but when it's you that's being threatened a punch is just as good as any sword.
Izumi likes to bring you along to his practice sessions with his unit, it's good to have some sibling support.
He taught you how to dance just like him and is always cheering you on as you try and learn.
Izumi likes taking you to Sibling Karaoke Night! You two sing the night away and it is the sweetest scene ever.
If you are ever stumped on what to wear gear not because your big brother knows what to do! He will go above and beyond to make sure you always look your best, even doing your makeup. Sometimes he calls in Arashi for second opinions when it comes to hair, makeup and cute trendy things.
He keeps a picture of you in his wallet at all times.
He lets you style his hair and give him "makeovers", he does not mind- if anything he finds it amusing.
Skincare nights with movies!!