наебнул википедии:

He displays a strange ability to be able to summon and control the body of a 15 meter class Titan. Eren believes this ability to be the result of injections given to him by his father after the death of his mother. He initially had little control over the titan body that he summons, and would attack anything that he sees while in this form but, after increased use gained full control.

и сразу все стало понятно, что все остальные титаны тоже кем-то засаммонлены, например местными гонднами-аристократами или наоборот, живущими вне поселения людьми.

а то как-то не клеилось.