To be clear Erina did plan to kill Schuer to gain her ability, because according to the book, that is usually how it can be passed to the next individual. Schuer knows the taste of poison because she had drank it before from Erina’s old assassination attempt. But Erina seemed to found a loophole through the book and was able to steal her older sister’s powers anyways. And here we are with Schuer trying to regain them back!
To be clear Erina did plan to kill Schuer to gain her ability, because according to the book, that is usually how it can be passed to the next individual. Schuer knows the taste of poison because she had drank it before from Erina’s old assassination attempt. But Erina seemed to found a loophole through the book and was able to steal her older sister’s powers anyways. And here we are with Schuer trying to regain them back!