You're not alone anymore - Magical Girls and Companions

Kaname Madoka
Madoka looks up to Mami. In fact I believe that Madoka is the first person Mami cries in front of. Mami tries to be a cool and strong senpai for her, but finds herself crying. In response Madoka promises that Mami's not alone anymore. This gives Mami some confidence which leads to her tying up Homura, resulting in her being too weak to defeat the witch. After Mami's death, Madoka becomes even less certain about becoming a magical girl. She has many wishes that are unnamed as to why she becomes a magical girl, but usually she is under Mami's tutelage and often fighting alongside of her with Homura. After Madoka's wish, Mami is revived because witches are erased from existence.

In another timeline, after finding out the truth of magical girls and witches, Mami states that the only way to end the cycle is to kill all of the magical girls and turns on her comrades. She sets out to kill her friends and then herself. In this timeline Madoka kills her to save herself and Homura.

Miki Sayaka
Sayaka respects Mami and always keeps her ideals in the back of her mind. She tries to fight for righteousness. She refuses to relent in her ideals and fights for very much the same reasons as Mami. Mami makes sure to find out whether or not Sayaka wants to wish for someone else because she genuinely wants to help them or because she wants the other person in her debt. Sayaka does not answer immediately and starts to take her wish into consideration a little more. After Mami's death, Sayaka becomes a magical girl to save her friend, in part becuase she was unable to save Mami.

Akemi Homura
Despite her rough demeanor, Homura likes Mami. She cherishes her guidance but believes first and foremost in protecting Madoka. She blames Mami for her own death, this could be due to the fact that Homura was tied up and could not prevent it. If Mami had listened, perhaps Homura could have helped her defeat the witch, thus saving Mami. Rather than dwelling on the past, Homura constantly reminds Madoka that the job is dangerous using Mami as an all too poignant example. In Homura's defense, she has encountered Mami in other timelines in which Mami acted as her mentor and later tried to kill her. I cannot blame Himura for being tired of it and for having to take a much tougher stance on her friends after having watched them die repeatedly.

Sakura Kyouko
Kyouko respects Mami's strength. She returns to the territory at Kyubey's beckon after Mami dies stating that the only reason she stayed out of it before was because of Mami's presence. At the end of the manga she and Mami are pictured together. They appear with Homura, but it is not clear if they work with Homura or not. I believe that Kyouko and Mami would have been a very effective team. What separated them was their ideals. Kyouko lost faith in fighting for others where Mami lived for it. I think that Kyouko had a hard time relating to Mami despite the fact that they could have understood each other's loss and loneliness very well. I believe that Kyouko was afraid of being hurt further by having friendships so it was much easier for her to be alone. I feel that she would have come to rely greatly on Mami and didn't want that to happen for fear of what would have happpened.

Kyubey
Mami contracted with Kyubey to save her own life. She then devoted her life to fighting for his cause, defeating witches. He used Mami like he used all the other girls, but in most cases Mami did not know this. She trusted Kyubey with everything she was but still cautioned new magical girls from making selfish wishes. Kyubey lacks emotions and tends to do what suits his goals best, Mami seems to be fine with this though she does not know his true motives. Often times when she finds out the truth, she becomes homicidal and suicidal as she tries to end the cycle. Kyubey doesn't seem to care either way.