If he required a mammoth amount of spiritual energy to contract a fey with the Barren bloodline, most of his spiritual energy was being used on Morbius. He only had enough to contract one normal fey.
If the fey with the Barren bloodline needed more spiritual energy than a normal fey, he would not be able to contract it.
Hence, he asked the Moon Empress, "Master, what are the conditions to contract a fey with the Barren bloodline? I don't have a lot of usable spiritual energy left."
The Moon Empress knew about his alternate identity as Black, so she knew he had contracted many feys.
She was not shocked that he did not have much spiritual energy left.
Despite his young age, Lin Yuan had already contracted many feys. The Moon Empress felt that he was already far ahead of all his peers.
