She ran an underground medical clinic in Munich without a license catering to underprivileged clients and those who couldn't afford traditional healthcare, primarily from the refugee community, in the absence of her more experienced father. Her family had emigrated from Vietnam to East Germany during the 1980s. Dr. Kenzo Tenma encountered her at her clinic during his endeavors to track down and destroy the evil Johan Liebert, having come there to get a tipoff on the circumstances behind the murder of Blue Sophie, where she was backlogged with patients in desperate need of medical attention. Tenma, as a medical professional, insisted that the patients should be taken to an actual hospital in light of their grievous injuries, but she angrily responded that it wasn't an option for them due to their social status. Initially, the headstrong girl refused Tenma's help, but relented and allowed him to help her perform several procedures on the needy patients. Gradually, she opened up to Tenma on her situation and, when Tenma had to leave, stating that he had to end a man's life, she worried about what might become of him. Later, she was among those who watched his arrest on television, commenting that he was an "inspiration" for her and hoping for the best in light of the circumstances. (Source: Monster Wiki)
Agari-senpai, a big shark rumored to the model for the movie Jaws. He's a "senpai" to Wakasa because sharks are the top amongst fish. Although Agari-senpai looks scary, he's just shy. He hides underneath the water with only his fin visible because he's so shy. He's too nervous to speak because he ends up scaring people when he opens his mouth and flashes his many sharp teeth. So he uses body language to communicate instead. (Source: shinkeikaku.wordpress.com)
The eponymous devil of the Devil Ring. In the past, he was the last King of the Shang Dynasty, King Zhou of Shang, Dixin.
A younger girl who is in deeply infatuated with Kanade with the point that she is almost stalking her. She is extremely wealthy and often tries to spend her money after the twins. She likes collecting old paraphernalia, junk and pictures that belong to Kanade, most of which goes to her makeshift shrine. Despite her overwhelming presence, the twins seem to like her. Yukino is amused by her and Kanade seems more irritated than anything, but they both seem to have some sort of affection for the girl. Initially, her presence was seen as a threat to Kanade as she assumed Sakuya was interested in Yukino. She became aware that Sakuya was madly in love with her when Yukino clears the situation up. Sakuya also was feelings for Isako Mikanagi shown in the spin off of the main story, where they share a kiss as a result from her confession when Isako moves away.