u/Glass_Molasses_5343

I just created a bracket of H2O and Mako Mermaids characters in case you're interested.

I’d have seasom 3 be a movie with Emma in it but Bella could be included too

I’d have Bella have a stronger personality like a more clear defined one cause I think her personality is a bit boring compared to the other girls

I’d have Cleo and her sister have like 2 episodes about their relationship and let her sister develop a bit

I’d stick to seasom 1 and 2 tails

I love the show for the fun tween drama it was, but If I could rewrite it in a perfect world, here is how I would have done the show. Also it would have 4 seasons.

I would have kept the OG theme song for every season.

Season 1

• I would not change a lot of things because Season 1 was really good, I would just change a few details.
• Each girl's tail would be a different colour. Purple for Cleo, Icy Blue for Emma, Red for Rikki.
• First, clarification on ages. Zane just did senior year, one year prior to the events of the show, while Miriam and Byron (who I would rename Ben because we need more normal-ish names XD) are in their senior year.
• Emma and Zane are maternal cousins.
• I would make Dr. Linda Denman an acquaintance of the Gilberts and the Bennetts, that way she can be a bit more present throught the season, and we could have more conflict as Emma tries to hide her secret from her and she starts to suspect her.

Season 2

• Again, this season's main plot was iconic so I would not change a lot of the main plot, just a few details.
• Byron and Miriam stay around for this season.
• The girls visit Louise Chatham at her retirement home sometimes.
• Byron decides to find new passions besides surfing, so he starts working at the JuiceNet Café. While he and Emma still like each other, sometimes they clash because he is more relaxed and has new ideas for the café, while Emma is more by the rules.
• Knowing that Rikki and Zane are a couple, Miriam shifts her attention to Byron and starts trying to get him to date her, creating a brief rivarly with Emma (tell me how that one would be), that ends when Byron and Emma start dating in Ep. 17. He also respects Emma and is not pushy about her secret and she eventually tells him in the finale.
• When the girls get their new powers Cleo gets wind, Rikki gets fire, but Emma gets lightning.
• We would see Zane and his father Harrison rebulding their bond.
• At the end of the season, Rikki and her father Terry move to a nicer house and she tells him her secret. Her dad would be so understanding and supportive and not cause her any additional problems. He would be of great help to all of the girls and come to the rescue when things get tricky with the other parents.
• Charlotte's tail would be brighter orange.
• Charlotte and her mother move out of town at the end of the season.

Season 3

• Ok, this season would have the most changes, but the main plot overall would be the same (the water attacks thing).
• Lewis and Max Hamilton would still work to find mermaid lore out.
• Emma and Byron get Rikki and Zane’s plot with running the café with Zane as a investor in it.
• I would still bring Sophie and Will to the plot, but I would also give them parents XD, maybe they could have Zac's house from Mako Mermaids. Will would start to get into mermaid lore, when during one of his swimming trainings he is saved by a mermaid (history repeats itself).
• I would scrap Bella but still bring in a new mermaid. Inspired by Mako Mermaids, let's call her Sirena. Sirena is a natural born mermaid, and is from a pod. She’d of course have strict parents which attempt to prevent her from interacting with the humans, as she is the youngest of three sisters. Eventually her curiosity gets the better of her and she decides to travel the human world and becomes a human. She is also the one that saved Will.
• Sirena becomes friends with Rikki, Cleo and Emma, and the mix actually works this time, as opposed to Charlotte. She’d be anxious around Will, to the point she can’t say anything without it being a jumbled mess. The girls would help build up her confidence while teaching her about life on land (to which she’d become fascinated with). Her tail would be green and she would have the powers of siren singing, creating plants underwater and her weather power is earthquakes.
• Rikki starts working at Emma's (the former JuiceNet Café) as a new employee, along the same time as Sophie. This creates conflict between the two as they clash a lot as co-workers with Sophie always trying to one up Rikki and tries to suck up to Emma all the time, which means that Emma and Rikki clash a lot too because Emma can't see Sophie's real self and thinks she is just good at her job.
• Sirena moves in with Rikki.
• Sirena still gets a work at Emma's with the band. And Will is trying to find out the mermaid that saved him, while falling for Sirena at the same time and become torn between "the mystery girl" and Sirena. Eventually he chooses Sirena, and she ends up telling him the secret.
• I think the whole thing with Sophie trying to get Zane would still happen. She’d be working at the cafe and would see Zane come in regularly, and eventually Rikki and Zane would inded break up.
• As Lewis still leaves at the end of the season, Byron ends up taking his place as the  solid companion for all the girls.

Season 4

• Takes place a few months after the end of Season 3.
• It centers around the girls's plans now that they graduated.
• Mako Island starts to get sick and lose it's beauty.
• Things change when Will acidently becomes a merman and gets powers.
• Sirena's older sisters, true-born mermaids Lyla and Nixie are sent to remove Will's powers and eventually upon finding out that Emma, Cleo and Rikki are also mermaids, start a "civil war" agnaist them with Sirena in the middle. While Emma, Cleo, Rikki and Will are more, Lyla and Nixie are more powerful as they are natural born mermaids and have the moon rings.
• The OG girls all keep their lockets. Sirena comes in with her crystal like usual, but merman Will is who gets to have a matching crystal necklace with her.
• Zane learns from Byron and Lewis and regrets even more how terrible he failed Rikki and the girls. He and Rikki's status will forever remain uncertain, but over the course of the season, he tries to help the girls in the conflict, by with Byron working with Max to find why Mako is getting worse. Nate ends up finding out about Mako accidently and becomes obsessed with it.
• Sophie also begins her redemption arc (somewhat) but never finds out Will's secret.
• Rikki starts to get really good at working at Emma's.
• Eventually, Sirena's father that is a merman and has the trident comes in and the conflict gets worse because he is the most powerful and doesn't aprove Will and Sirena dating.
• Both sides are able to make peace and stop their conflict when they realise they are hurting Mako Island even more. Nate takes this chance and steals the trident, becoming the show's final antagonist so he can rule Mako Island with the trident.
• Everthing comes ahead in the finale, where everyone as to 1) use their powers to heal Mako Island and 2) stop Nate's goals. While Sirena, Lyla, Nixie and their father use their powers to heal Mako and protect it from the effects the following fight will cause, Emma, Cleo and Rikki take the Moon Rings and head to Mako to stop Nate. The three (alongside Will) come together with their powers and destroy the trident, preventing Nate from executing his plan. 
• Following the battle, Lewis returns to reunite with everyone and Nate tries to tell everyone the secret but everyone thinks he is crazy.
• Sirena decides to stay on land with Will and her family agrees to it as long as she comes back to visit the pod regularly (and vice versa). She also decides to stick with the band. Her father also officially names Emma, Cleo, Rikki and Will part of his pod, if they ever need help.
• Cleo decides to go to school in the US with Lewis. Emma names Rikki the new person in charge of the café and alongside Byron and her family decide to travel the world (where she will finally tell them their secret), Rikki becomes the new owner of the cafe and makes extra money with finding artifacts in the ocean. 
• The show ends with Cleo, Emma, Rikki, Sirena and Will all running off into the ocean with Lewis and Byron on a boat, and head off to Mako for their own party. They all promise each other they will have each other's support forever, no matter where they go in life. Mako keeps them united forever.

So there it is, give me your thoughts!