Mimmi and Ondina are best friends, but often don't get along when Ondina thinks she can do things on her own and never listen to Mimmi. They have both returned to Mako from the pod thinking Zac will still try to take over the moon pool. Mimmi often has to get Ondina out of sticky situations when she goes off by herself convinced she can do everything on her own. Neither of them trusted Sirena initially due to her connection to the land and friendships witht with Rita and David, but eventually they have to give in and get legs to complete their mission of breaking Zac's connection to Mako. Sirena eagerly takes them in as friends, having been lonely without Lyla and Nixie. The three mermaids develop a bond through the series.
Mimmi is a northern mermaid, who came to live with the Mako pod in Australia and is the daughter of Nerissa. She and Ondina are loyal best friends. Although she typically follows Ondina's lead on things they do, she does not hesitate to speak up to her when she is out of line. When she and Ondina return to Mako to try to save it for the pod, Mimmi learns to trust Zac much more quickly then Ondina does. Throughout her time on land, she is eager to learn as much about his new world as she can. Mimmi would also learn much more about herself during this experience. Throughout her time on land, it becomes apparent that she shares some sort of connection with Zac, as they share visions. At first, the mermaids and Zac believe that his connection to Mako Island is causing this. This theory is later proven incorrect and the connection is revealed to be not through Mako, but through blood. It turns out that Zac is actually the son of Nerissa and Mimmi's long lost brother. This revelation shocks Mimmi, but she does not hesitate to protect Zac when Veridia attempts to do away with him. Although she and Ondina are cast out of the pod for this, she hardly cares as she has now found an important piece of her life she somehow always knew was missing. Unfortunately, Zac is not as enthusiastic about this as she is since it means his whole life has been a lie. Although somewhat saddened by her brother's rejection, she remains confident that he will eventually come around and accept her as his sister. Following this, Mimmi attempts to form a relationship with her newfound brother, but Zac still wants nothing to do with her. While trying to be understanding, Mimmi cannot help but feel a little frustrated since she is also hurting from her own abandonment while Zac has had a family in the Blakley couple. She later confronts him briefly on this when Zac unleashes his anger on two obnoxious lifeguards. When Zac is able to come to terms with who he is after talking with his parents, he is also finally able to accept Mimmi as his sister much to her delight. Throughout the second half of season 2, Mimmi is shown to have developed a strong bond with her brother similar to Sirena's bond with her sister Aquata. As Zac' curiosity of the chamber grows, Mimmi refuses to go against his wishes and completely trusts that Zac will allow no harm to come to her or any mermaids. She also wanted to accompany Zac when he starts the chamber to ensure no harm comes to him either.
Mimmi also gains a love interest in a young man named Chris after deciding to get a job at the marine park. At first, he rubs her off the wrong and comes off to her as unreasonably strict when he scolds her for being in an employee only part of the park while talking to a dolphin. Later, she finds out that he has a passion for dolphins and dreams to work with them, but he is unable to form a connection. Mimmi resolves to help him and successfully gets him into the training program. They then share a kiss, but nothing apparently would come of it when she learns that he will be in America for 3 months. Though he assures her that they will see each other when he gets back.
Later, Mimmi would face more complications involving the people she cares about. As Ondina and Erik spend increasingly more time together, she also spends increasingly less time with Mimmi sparking jealousy. This would eventually cause them to have a fallout, although they do make up. Later, when Veridia allows them to return to the pod, Mimmi struggles with the possibility of never being able to venture on land again and having to give up on the only family she has ever had in Zac. Her strain only grows when Ondina decides to give up on the pod for Erik, causing a much worse fallout. They later make up and decide they must find a way to convince the pod that land people and mermen can be trusted so that they don't have to choose between the people they care about.
Danger soon starts to fill the air after the group discovers that the trident stone is the key to starting the chamber and when Zac accidentally causes it to become active again. Despite Zac's and the mermaids best efforts, Erik is able to gain possession of the trident stone and Mimmi is horrified when she witnesses Erik use the stone to steal Zac's powers and render him unconscious. Erik is then able to escape with the stone while Mimmi tends to her brother. Despite Mimmi's attempts to encourage him, Zac seemingly gives up hope leaving it up to her, Ondina, and Sirena to stop Erik. Their attempt to stop the chamber fails and it slowly begins to kill them. When Zac seemingly sacrifices his own life to stop the chamber, Mimmi is devastated by the apparent death of her beloved brother. Desperate to save him, she puts her own safety at risk again when she attempts to use the stone to heal him despite previously experiencing the effect it has on mermaids first hand all while tearfully begging him not to leave her. She is successful and Zac's life and powers are restored, to her great relief and happiness. The pod then returns to Mako and Mimmi swims off with the others to greet them, overjoyed at now being reunited with both her pod, and her brother.
Mimmi is a gorgeous mermaid from the Mako Island pod. Sweet, but self doubting and clumsy, she is extremely intelligent and always seems to be soaking up knowledge without even trying.
Mimmi has long wavy brown hair , with very tanned skin and grey eyes. Like Sirena, she usually wears girly dresses and skirts and cute tops. Mimmi commonly wears outfits with flowers or nature-type patterns. Coincidentally, Mimmi is very similar in looks and wardrobe, to Cleo Sertori.
Mimmi possesses the ability to transform into a mermaid ten seconds after physical contact of water. She turns back into a human several minutes after climbing out of the the water and once her body is completely dry, she turns back into a human along with the clothes she was wearing before she transformed. As a mermaid, Mimmi has the ability to swim at a super speed of 600km/h, hold her breath for more than fifteen minutes, and dive deeper than any ordinary human being.
"In The Seventh Cycle", Mimmi and Ondina used this ability to send Cam flying.
Zac and Mimmi are able to share visions, being siblings.
In "Sticky Situation", she used this ability to take Evie's essence.
In "The Truth About Evie", When she sneezed, she produced a small patch of snow.
In "Surprise!" Mimmi used this power to lift a water bubble.
Mimmi used this power in "The Siren" to a heat Carly's phone.
In "Careful What You Wish For" Mimmi used this power on Cam to get the cold water out of his body.
- Mimmi regularly practices potions and spells using resources in Rita's grotto.
- Mimmi always wears a silver necklace with a dolphin pendant.
- Mimmi is fluent in the language of the humpback whales. It is also mentioned by Ondina that she would often stop to chat with dolphins as well. She is also seen communicating with a dolphin at the Marine Park.
- Mimmi sings in the moon pool, though not as often as Sirena does.
- Mimmi took a special class on enlargement in mermaid school.
- There is a distinct possibility that Mimmi is the eldest of Nerissa's children but it was never confirmed in the show. She could also very well be Zac's twin sister.
- It is confirmed that she will reunite with her love interest, Chris, in season three.
- Mimmi is very similar to Cleo, both of them had a job at the marine park, and both of them are the brown haired in the iconic mermaid trio found on both H2O: Just Add Water and Mako: Island of Secrets
- Mimmi is probably immune to Snow Rash, since she is a Northern mermaid.
- Mimmi is the first ever non-Australian main character on the shows H2O and Mako. Although Mimmi possibly could be portrayed as an Australian mermaid, the actress Allie Bertram keeps her original (Canadian) accent onscreen.
- Mimmi thought Erik stole one of Rita's pendants to sell so he could make money for a party for Ondina.
- Mimmi acquires more and different powers to the Australian mermaids because she is a northern mermaid.
- Mimmi is fluent in the language of the humpback whales.
- Mimmi sometimes sings with Sirena, as seen in the ending of season 2 episode 9 "Stowaway".
- Because of Nerissa being her mother, Mimmi is considered an extremely powerful mermaid even to Viridia.
- She and her brother Zac are royalty.
- Mimmi is an expert at a duplication spell that specialises the moon ring.
- Mimmi states that if Evie were in a pod, she would be very close to getting her moon ring.
- Since she's a northern mermaid, she's immune to the northern mermaid siren song.
The image gallery for Mimmi may be viewed here.