Mermaids have a special constitution. Even upon reaching adulthood, they do not differentiate automatically.
For a Mermaid to differentiate, there are only two scenarios—
One, the Purification Holy Medicine can induce differentiation. After drinking the medicine, the Mermaid's body will experience excruciating pain, as if being torn apart. This agony lasts for seven days and seven nights, at the end of which they will have differentiated a pair of human legs.
Two, the Mermaid differentiates voluntarily, even actively seeking it out. In this case, their fishtail will feel a tingling, electric sensation, unlike the tormenting pain of a forced differentiation.
However, very, very few Mermaids are willing to differentiate voluntarily.
Even with the blood of the Enchanting Sharks flowing through their veins, they are unwilling to become slaves to their desires.
This time, the Mermaid, Yusen, was differentiating voluntarily.
