Mercy Olubunmi (previously Chubb) is one of four main characters in EastEnders: E20, alongside Zsa Zsa Carter, Leon Small and Arthur "Fatboy" Chubb. She was the only character from the spin-off to not automatically be transitioned into EastEnders. It was subsequently announced that she would join EastEnders due to positive reaction to the character, and made her first appearance in the soap on 31 May 2010. She is the ex-wife of Arthur Chubb and daughter of Grace Olubunmi.
In EastEnders: E20 series one, Mercy, who is friends with Fatboy, is trying to create a project for the local church with the youth minister Benjamin (Damien Lynch), and if it is successful, Mercy's grandmother (played by Jay Byrd), will fund her university place. She enlists Fatboy's help but his ideas leave them humiliated. Mercy, along with Fatboy, Zsa Zsa Carter and Leon Small, ends up squatting in 89b George Street, where she takes a pregnancy test and then tells her grandmother she will not be coming home. The next day, all the E20 gang are locked outside the flat so they steal the key from Lucy Beale and Mercy
plays drunk as a distraction. Mercy later visits a clinic to discuss about an abortion and tells Fatboy that she is pregnant. It is later revealed that Benjamin, who is married to Celia (Marsha Henry) is the father, but Fatboy accuses Leon of being the father, and after an argument, Mercy doubles over in pain and it rushed to hospital. She suffers a miscarriage which Benjamin seems to be pleased about and he then says that it was probably for the best. When she returns to the flat, Fatboy looks after her and she later attends Leon's boxing match. During the match, Fatboy gives Mercy a completed project for the church. When they find out that Amira Shah is returning to the flat, Fatboy invites everyone to stay at his home, but Mercy decides to stay with her grandmother. She later leaves London to go and live with her parents in Nigeria.
In series two of EastEnders: E20 Mercy only makes a cameo appearance when she witnesses an argument between Fatboy and Naz Mehmet and eventually Zsa Zsa also gets involved with the argument.
Several months after the events if E20, Mercy returns to Walford following a few months in Nigeria to meet Fatboy but he isn't there. She later overhears a conversation between Darren Miller and Billy Jackson and she finds out that Fatboy is a party in Hampshire, so she travels there with Billy. Mercy and Fatboy are extremely pleased to see each other, but as soon as a fight breaks out between Peter Beale and another guy, they escape into Fatboy's van, Billy leaving his motorbike behind. Peter has to drive since Fatboy is too drunk to drive but he hits something by accident. The next morning, Mercy is reunited Zsa Zsa and Lucy but they soon realise that Leon is missing. After searching for him, they find his mobile covered in blood. Peter, Fatboy,
Mercy and Billy suspect that he could have been run over by Peter. Mercy suggests going to the police. The gang visits the police and Fatboy is about to admit to running over Leon until Leon suddenly appears at the police station. The gang are relieved to see him. They decide to pull a prank on Lucy for lying to them about Leon. After arriving back in London, all the gang pretend that Leon is still missing and visit Lucy. They then sent a text message to Lucy saying "If you want to know what has happened to Leon come to the park at midnight." Lucy visits the park at midnight only to be ambushed by two men. The two men are revealed to be Leon and Fatboy. The rest of the gang come out of the bushes and tell Lucy to stay away from them. Mercy's grandmother, Grace returns to Walford and urges Mercy to tell Fatboy that Mercy is will be moving permanently back to Lagos, however Mercy cannot find the right moment so Grace just tells Fatboy instead. At Grace and Mercy's leaving party Fatboy soon realises that neither Mercy nor Grace want to leave London, and after Mercy hands in the keys to their home, he gets them to meet and helps them to realise it for themselves. Although Mercy and her grandmother are now homeless, Fatboy says he has a plan.
After an argument between Fatboy and Mercy, she pushes him and he falls onto the tree planted in memory of Trina Johnson causing it to break. Worried that Trina's ex-husband Lucas Johnson will be angry with them, they enlist Leon and Zsa Zsa's help to replace the tree. However, as they dig up the tree, they discover Owen Turner's body buried beneath it. The next day, Fatboy comforts Mercy when she says it is all she can see when she closes her eyes. Mercy attends Lucas's Bible class and questions him about false prophets and a passage that states that anyone who questions a priest should be put to death, however Lucas cannot answer and he makes an excuse to leave. Grace is angry and orders Mercy to write an apology to Lucas however she throws it away. Mercy and Fatboy play rounders but they smash Dot Branning's window. Fatboy attempts to repair it but he does it badly so Dot calls a professional. Mercy later asks Dot if she can attend her church and Dot offers to let her come with her. Mercy later plays rounders along with Fatboy, Max, Jack, Darren, Liam and Abi and they all witness Lucas being arrested after holding his family hostage. Mercy asks Dot if she can join her church after she is initially confused about Catholicism and Lucas' actions.
When Zsa Zsa is left homeless she asks if she can move in with Mercy and her grandmother. Leon and Fatboy visit Mercy's home but they accidentally break one of Grace's commemorative plates. Mercy is blamed but Fatboy eventually confesses that it was his fault. When Alfie Moon sets up a drinking den in the cellar of The Queen Victoria public house, which is closed due to being burnt down, Mercy and her friends attend and Alfie gets Mercy to serve the drinks whilst he is not there. Later, Grace tells Mercy that she cannot work in an illegal drinking establishment and blames Fatboy for corrupting her. Mercy soon learns from Fatboy that Leon had slept with Glenda Mitchell and she tells Zsa Zsa who was planning to go to France with him. Zsa Zsa and Leon both leave, but separately, leaving Mercy and Fatboy upset at the loss of their friends.
- Mercy was originally only meant to be an EastEnders: E20 character only, but due to the popularity of the character, Diederick Santer decided that she would appear in EastEnders as well.
- Mercy was the first character in EastEnders to call Fatboy by his real name, Arthur.