The Story of the Growing Water Child 「水の娘成長物語 Mizu no Ko Seichō Monogatari」 is the 58th Page of Yūki Tabata's Black Clover.
Asta and Noelle Silva are watching a girl singing by the ocean, and think about how she has a beautiful voice. The girl notices both of them and screams in embarrassment. She heads over to their spot introducing herself as Kahono and asks for their names. Noelle introduces herself and Asta as "Dumb-sta", which Kahono thinks is a unique name, but Asta explains that Noelle is just insulting him. Noelle asks what Kahono was doing here, and Kahono reveals that she was practicing her singing and that she wants to become an idol. Asta and Noelle ask what an idol is, and Kahono that it is the latest trend at the royal palace and that she is in it for the money. Kahono notices that Asta looks a little drained and uses her Song Magic to heal him. Asta and Noelle are amazed by how good her magic ability is. Kahono tells Asta that each heal with cost 100 yule, which shocks Asta, and he pays with the last of his money. Kahono then asks how old they are, and they reveal that they are 15. Kahono reveals that she is 15, too, and asks to be their friend, to which they agree.
Kahono then advises Noelle not to suppress her magic, and Noelle is shocked that Kahono noticed her practicing. Kahono says that she can become relaxed and use her magic as she pleases after hearing the waves. Kahono also says that true concentration comes when one's mind is at peace. Asta agrees and adds that his best swings are when he does not think. Kahono asks Noelle about her best memories and about her family, but Noelle just remembers that her family disparaged her for being weak since birth. Noelle then decides to go back to training.
For the next few days Noelle practices her magic, while being cheered on and helped by Asta and Kahono. On the night of the full moon, Noelle is still unable to control her magic, and Kahono cheers her on. Asta tells Noelle that he remembered when her magic went out of control and that she should just release all of her magic. Noelle says that it will not go right, but Asta replies that he will just help her out. Noelle gives in and releases all her magic. She thinks about how she is losing control and that she knew she was going to fail. A she begins to lose consciousness, she suddenly hears the other Black Bulls cheering her on. She remembers all of the good memories she has had with the Black Bulls and manages to control her magic, completing Sea Dragon's Cradle. She is glad that she is able to control her magic, but loses her concentration and falls. Asta manages to catch her and tells her that she did a good job. Yami Sukehiro looks pleased and says that it is time to go. Noelle starts to look for Kahono but cannot find her. Kahono is watching Noelle and says that Noelle has some good teammates. She also says that she will be waiting to see Noelle at the Seabed Temple and leaves.