FAIRY TAIL GUILD -
Most members of Fairy Tail are afraid of Erza, who often criticizes their bad habits, leading them to apologize to avoid her wrath, but like most Fairy Tail members, she shows great loyalty and dedication to Makarov and the guild, proven by her pushing herself past her limit in the war against the Phantom Lord Guild and fighting against its many powerful members. She also became the temporary leader when Makarov had to be treated because of his scattered magic. It was also shown that she is furious whenever the guild or any of her close friends is underestimated or insulted. She is unafraid to defend them, showing a great deal of her love and kindness for them.
NATSU DRAGNEEL -
Natsu and Erza seem to have a close relationship. Erza stated that him, Gray and her even used to shower together. He often thinks that Erza is scary though wishes to beat her someday. Despite this, they care about each other very much. On the Lullaby arc, Erza had to knock Natsu unconscious since she knows that Natsu has motion sickness and that it'll help him until they reached their destination. With the interruption of their fight, Erza got arrested by the council, not knowing it was just a formality. Natsu sneaked out from the guild and disturbed her trial by crushing into the council courtroom, comically dressed as her in which resulted that both of them got thrown in jail. Despite being angry with him, Erza was grateful that Natsu cared enough to try to help her. During the Phantom Lord arc, Erza encouraged Natsu to unleash his true power to save the guild and she also told him that he may surpass her one day. In Tower of Heaven Arc, Natsu fought Jellal in order to to protect Erza from him and due to the pain that Jellal caused her which enraged Natsu to defeat Jellal eventually. Natsu saves Erza after her attempt to sacrifice herself to stop the Tower of Heaven from exploding. Natsu then says to Erza not to risk her life again by doing such things like that so recklessly. Erza trusts Natsu to the point that she relied on him to defeat Laxus in the Fighting Festival arc as she tries to destroy the Lacrima chrystals that surrounds Magnolia as the Thunder Palace was about to be activated. Erza also mentions that she will come back safely since she will not risk a life which he once saved. When Natsu discovered that Jellal was still alive in the Orasion Seis arc, he wanted to take him out quickly to make sure he doesn't meet Erza again. Though in the end, he defended Jellal from being arrested by the Magic Council for Erza's sake.
GRAY FULLBUSTER -
Gray and Erza are very good friends and they care for each other very much, Erza stated that him, Natsu and her even used to shower together. However, Erza is usually annoyed by Gray's stripping problem to the point where she beats him up when she saw him walking around half-naked.Their relation goes back to when Erza first joined Fairy Tail. Initially, Gray did not like Erza because she would always be alone and wears an armor every now and then. But his attitude towards her changed when he challenged Erza to a fight and saw her crying instead. Rather than challenging her, he changed his mind and asked Erza why is she crying and why is she is always by herself. Gray had also pushed himself to the limit in his fight against Fukuro in order to hurry up to save Erza. In the Oracion Seis arc, Gray stalled Racer through using his Ice-Make magic and create a barrier (Ice-Make: Rampart) for Natsu to save Erza with Wendy's Healing Magic. Gray saying he'll handle Racer and that it's more important to save Erza than to worry about him.
LUCY HEARTFILIA -
Lucy admires Erza's strength and beauty. She really considers Erza a role model and cares for her as a true friend. Likewise, Erza cares a lot for Lucy, as seen when she dueled Master Jose of Phantom Lord and defended Lucy because Phantom Lord was merely using her name to acquire money from her family. Erza also has expressed fascination with Lucy's choice of undergarments when she and her teammate stayed in Lucy's apartment.
Like Natsu, Happy thinks Erza is scary but Happy admires her strength and magic. He calls her magic pretty as her opponent's blood goes everywhere. Erza knows Happy since he was born, being present when his egg was hatch when she was still young.
Another S-class mage who used to be Erza's archrival. Erza's rivalry with Mirajane is a lot similar to Natsu's rivalry with Gray. When they were younger, Erza and Mira pick a fight everytime they see each other. However, since the event of Lisanna's disapperence, Mirajane's personality changed. Mirajane's attitude towards everyone, including Erza, have changed and she and Erza get along very well.
GAJEEL REDFOX -
Like the rest of Fairy Tail, Erza expressed her doubts when she realized that Gajeel has been aggregated into their guild by Makarov himself, specially considering his past involvement during the Fairy Tail -Phantom Lord Guild War. However, she does seem to be willing to set them aside since it was her Guildmaster's decision to have the former Phantom Lord member as part of Fairy Tail. But she insisted that Gajeel must be kept at constant surveillance, to which Makarov agreed. She does seem to genuinely trust Gajeel, as seen during their escape from Edolas, where she entrusted Gajeel the task of reverting everybody in Fairy Tail that were converted into Lacrima back to their original states. Still, this did not stopped her from pulling some strings that prevented Gajeel from being chosen among the S-Class trial contestants. Afterwards, it was revealed that she was the one behind the plans, feeling it was too early for Gajeel to be a S-Class member of the guild.
WENDY MARVELL -
During the formation of the Light Team, Wendy was the last person to have arrived. She was so in a hurry towards the rendezvous that she tripped down in front of the other mages in the process. As Wendy got up, she introduced herself to all of them while others remarked on how young she was to have joined a dangerous mission like this, including Erza herself. But, after her introduction, Erza apologized towards her comment and said she is happy to have her in the team. Wendy then concluded that Erza was nicer than the hearsays have said, as well as Charle. During the battle with Oracion Seis, Wendy was the one who saved Erza when she got poisened using her Healing Magic. Later, when Wendy finds her with Jellal, Erza stated that she was thankful to Wendy. In the end of the Oracion Seis arc when Cait Shelter Guild revealed to be illusion, Wendy was crying when everyone in her guild disappeared. After all of Wendy's fellow Cait Shelter guild members disappear, Erza comforted her and invited Wendy to join Fairy Tail.
JELLAL FERNANDES -
Erza and Jellal have a complex relationship. They were friends in their days of slavery. During those times, Erza looked up to his sense of justice and courage. Jellal cared for her to the point of going to the dungeons by himself to save her. Jellal was the one who inspired Erza to fight and gain their freedom. However, when Jellal was brainwashed by Ultear (the so-called "Spirit of Zeref"), he became a totally different person and exiled Erza from the Tower of Heaven, making everyone believe that Erza had betrayed them. In the Tower of Heaven Arc, Erza and Jellal fought. Erza described herself as someone who always cry since she failed to protect those who are dear to her. Both instances where Grandpa Rob who saved her from destruction and Jellal who also saved her, resulting from him being taken and was brainwashed by "Zeref". When Jellal asks Erza to strike him down since the R-system could not be finished and that no one could save him, she refuses and hugs him instead. Erza, not realizing it was only a trap, was contained in Jellal's Serpent Binding spell that was set when they both hugged to prevent her from moving a single muscle. When Jellal almost sacrificed her to "revive" Zeref, he claimed that he loves her and forcefully pushed her towards the R-system crystal. Fortunately, Natsu saves her. In spite of everything, Erza seems to have feelings for Jellal since she knew Jellal might be the one responsible for saving everyone from the tower's explosion. During the Battle of Fairy Tail at the Fighting Festival arc when Mystogan fought Laxus, Erza was seen teary-eyed and about to cry when Mystogan resembles Jellal. Not knowing it wasn't Jellal, she became emotionally unstable for a moment . In Oracion Seis arc, Erza discovers Jellal is still alive and runs off to look for him, but when she finds him she realizes he had lost his memories. When Erza finds out that Jellal plans on committing suicide to make her pain go away, Erza forcefully confronted him that he must continue living and declares in her fight with Midnight that she can see the light inside him. After defeating Nirvana, Erza tells Jellal that even if his darkness resurfaces, she will always be there for him and saying he doesn´t need to care about his memories. At this moment, she then says "I..." and was unfinished since the Council Army arrives to take Jellal and Hoteye away. Erza is seen trembling when everyone is fighting for Jellal's freedom, though she understands his feelings and lets the Council Army take him away. Jellal then mentions her last name "Scarlet" before he left. Later, Erza was seen crying alone over the loss of Jellal, remembering when he gave her her last name after the color of her hair, so that he would never forget during their days of slavery; Jellal saying back then "It's the color of your hair. That way, I'll never forget it.". The sky then appeared in a deep scarlet color as she dwell within her memories of him.