Blue star dragonball is dragonball that summon dragon and use the ability sync link if the user have been acknowlege by their dragon. One of the three strongest dragonball.They collect negative energy the more the user use it
Spoiler!
They choose their owner. When all 7 are gather, they can summon the strongest combat dragon, Soulillk that source of it attack are the negative energy of the 7 dragonball thus the more it use the less powerful it attack is but can purify the negative energy.