You called him "Kuya" because he's you Brothers friend and older than you.

Now your brother bring you to them going to the mall, when Ran tease you while you guys are walking.

Ran: bunso? Why are you so small~?

You: shut up kuya Ran!

They just laugh,and continue to walk.

You guys are buying some clothes,you just sit there since your done buying when Ran approved you, holding a cute dress.

Ran:hey... this would look perfect on you,Bunso.