nhk world niha gupta has this report. >> reporter: schools of kites fly in the sky. this is a festival to celebrate the arrival of spring. kite flying is a long-loved tradition but also a competitive game. they try to cut the kite strings of their opponents. the pink kite battles against the blue one, but the string is severed and it falls towards the ground. one family has prepared 400 kites for the festival. relatives gather for the event every year. >> this is the importance of the -- we get together and fly kites and loud music and we all party together. this would obviously get the family together. >> reporter: special strings are used in competitive kite fighting. this white powder is finally crushed glass. it is dissolved into liquid and applied to the strings. when it dries, they become sharp enough to cut opponent's strings. strings produced through this procedure are called manga. there's a higher demand for stronger and sharper manga for this kite fighting competitors. this is a glass coated thread in my hand. this could easily cut thread. but this can cau