it doesn't store haki it just makes the person able to use ryou without training.
The sword makes it harder for you to use haki or ryuo. If you can not use it before you're not going to become instantly better at it by just using enma.
That's like believing wearing a weighted vested will instantly make you faster. It won't. The vest can help you become faster by training with it but you won't get an instant speed boost by wearing it.
Zoro has been using haki or ryuo since his battle with Mr. 1. His haki improved a lot during his training with Mihawk. Yet, the first time he used enma he had problems controlling his haki.