It was all in the breathing, but not to focus on it too much, or he would end up chasing the thought of breathing in an overly conscious way.
Leonard followed Seraphis's instructions. They were clear enough for him to execute easily, but with each passing second, he found it harder not to overthink. He was probably worried that his efforts and the Basic Summoning Scroll would be in vain.
Hell, it would hurt if it all went to waste.
But soon enough, Leonard realized that such thoughts were only distracting him. He learned not to chase them and instead drifted mentally, scanning his body without putting too much effort into it.
It felt like he was dancing while sitting, his body subtly moving up and down with his breathing, until he gradually ignored the fact that he was still breathing.
Even though breathing was essential in meditation, the key was to sense the entire body. After a few minutes, he began feeling his scalp and, eventually, his toes.