Why put trust into people all they will do is break you.
Personality
Ling is always alone he tries to avoid getting near people and is worried about people betraying him. He will not trust a meister and be used until he completely trusts them and even then the slightest thing could mess his trust up. He tries to tell people he doesn't care if he has a meister but they don't believe him. He tries to shoulder the weight of his own problems but after a while if they are not dealt with every thing comes crashing down on him. He tries to take the very early morning and terribly late night shifts at the cafe to avoid other people he gets there so early and leaves so late he was given a key to the cafe.
School supplies, cafe key, ....(more to be added later probably.)
History
The first meister Ling got abandoned Ling so he could escape a Kishin the shock broke Lings true weapon form and caused him not to trust people. The Kishin attacked the meister and was then beheaded by Ling. Ling did not eat the Kishin soul but went on a killing spree and devoured all the human souls he could find after finishing the 99 soul he came back to his senses and swore not to eat another soul again till he found who deserved it.