Death[]
Madelyn is first introduced to Death upon being monitored then brought in by Sid and his partner. Death finds her to be rather playful and stubborn, but enjoys and respects her abilities to control and suppress her pull of magic upon willpower. He enjoys her pranks and allows her to go full blast with them on Halloween Eve and during October to which she always dresses up as a black cat.
Death the Kid[]
Madelyn is introduced to Death the Kid by his father, Death, and takes it upon himself to watch over her and monitor her so she never had to worry about shelter or anything else. Initially he despises and detests her, especially after realizing she constantly pulled pranks on him and made things appear asymmetrical with her illusion magic just to agitate him. After coming to respect her over time and developing feelings for her which he later reveals as actual "love" for her after Asura's defeat, he learns from Liz that Maddi actually has had a crush on him for some time and pranked him to hide that fact since she couldn't express that part of herself in fear of getting hurt. The two are productive towards one another as Maddi tends to help him adjust with his madness of order, while Kid in return allows her to continue living without fear of falling back into madness or the pull of magic. Kid also dressed her up for every party and ocasion he believed was important, insisting she needed to look her best.
Liz and Patty Thompson[]
Madelyn annoyed Liz rather often due to her making Kid agitated often enough that she had to deal with his obsessive tendencies after bickering to her about Maddi's antics and being a complete and utter troublemaker. Upon actually getting to know Maddi through missions in which Kid insisted she tag along, she began to enjoy Maddi's company since she took a load off her back when helping Kid deal with his Madness of Order on several occasions. Patty often enjoyed Maddi's pranks and thought she was rather funny, but did grow agitated towards her on one occasion when Liz yelled at Maddi to which Patty backed her up. After finding out that Kid had fallen for Maddi, she proceeded to sing, "Kid has a cru-ush, Kid has a cru-ush." and "Kid and Maddi sittin' in a tree, k-i-s-s-i-n-g" before Kid asks if she was seven due to her childish nature on the subject from embarrassment.
Maka Albarn and Soul (Eater) Evans[]
Madelyn doesn't get along with Maka very well even unto this day, though their relationship progressed from sheer detest and hatred for one another to a loyal friendship and rivalry. Maka has only made Maddi cry on one occasion before their truce. Maka appreciates her loyalty above all else. As for Soul, he prefered that Maka not agitate her since she was the only witch before discovering Kim was a witch that didn't enjoy terrorizing humans and meisters for their souls. He thought her pranks were often "uncool" unless they were played on others. On one occasion he thanks her for trying to help Maka when Maddi tried to fight Crona in her place, and told her she didn't need to worry about it that she failed to defeat him.
Black Star and Tsubaki Nakatsukasa[]
Black Star often was chill with her pranks unless she pushed him too far to which he threatened to feed her soul to Tsubaki after he killed her. After coming to good terms with him because of Tsubaki telling Black Star she wasn't as bad as she acted out to be, he realizes she's kind of similar to him and learns to respect her in that way. Tsubaki often went to Maddi when things were going wrong for her. She gave Maddi plenty of advice, and often about Kid and Maka due to their initial hostility towards her before they warmed up to her. Tsubaki proven correct upon explaining that everyone would come to love her as a dear friend upon getting to really know her.
Stein and Spirit[]
Maddi initially annoyed Stein and he kept her quite often after class for detention due to her troublesome shenanigans during class time. On one such occasion that she performs a nudity illusion spell, he appears naked except for a pair of boxer shorts to the whole class and himself before he takes her outside and is affected by her soul's wavelength and goes into temporary madness before almost cutting her open. Upon regaining his sanity, he realizes Maddi was already under the control of madness and the effect of the pull of magic before trying to talk her back into her own sanity before becoming injured just when Maddi kicked him to get away and get out of the city. Spirit often suffered from pranks due to Madelyn and one such prank involved him seeing her as a beautiful 21 year old woman with a nice body before he asks her to go on a date with him at Chupacabra's. Upon realizing he fell for another one of her pranks, he gets angry at her before noticing Maka was behind him having seen the whole thing. He then begs at Maka's feet to forgive him before she kicks him and states he's a sorry excuse for a man and a death scythe as well.
Free and Eruka[]
Free finds Maddi to be a challenge and preferred to fight her over Maka and the others due to her unpredictable abilities and movements. The two also have a completely opposite relationship on Maddi's side as she openly states she wished he'd just go back to his jail cell and rot for another 200+ years after having met him once after his escape, to which he tried to convince her to fight him and see how powerful she was, sensing her unstable soul wavelength and anger towards him, as well as realizing she is a member of the Blackwood Family which feuded with the Immortals some centuries before his capture and detainment. Eruka finds her to be a sorry excuse for a witch until seeing her true prowess under Arachne's control. She attempted to tempt her into joining Medusa's army before having to retreat due to almost being blown up by Madelyn's cat bombs, similar to Eruka's tadpole/frog bombs.
Medusa and Crona[]
Medusa wanted her to join side with her and her followers upon realizing her potential while allied with her sister, Arachne. She fails to recruit her however due to Eruka's need to flee before she tries to have her killed on two occasions. Crona fought Madelyn before Asura's revival and took her down with a single screaming resonance. Crona then shows regret for harming her and reducing her to her cat-state after Maka connects with him and offers to take care of her till Maka and the others returned, but Maka insisted Kid and the others would want to make sure she was okay and Kid would want to monitor her himself incase she was hurt more than she seemed to be. Crona has a hard time dealing with her sometimes due to her initial playful nature.
Arachne and Asura[]
Arachne, upon now owning her like a master owns a pet, constantly pet and groomed Madelyn while she was in her cat form until needing her to run errands for her. Arachne often enjoyed stroking under her chin to get her to purr and notes her as "cute" and "adorable" on two occasions when speaking of her as a mere pet to Kid and the others.
Asura, however, after devouring Arachne's soul, makes Madelyn into a mindless puppet filled with a soul he stated that he would devour in front of the others before being engaged in battle and forced to ignore Madelyn for the time being until he's finally killed. He, only once, refers to her as a cute little "snack" to Death the Kid and his friends, knowing that it would spark agitation within them and bring them to fear that Maddi would die before the battle was over before they got her body to a safe place along with Spirit and the others so she could rest and recover if they managed to kill Asura, which they did.