I was rewatching H2O season 1 when I realized something: when you think about, each original character has had their own season that sort of resolved around them. Let's start with the beginning:
Season 1: Emma
You may or may not have noticed but the one who always gets seen by Zane is Emma. She is the one who saved Zane, she is the mermaid that Zane saw twice (during his saving and with her red hair) and in the finale she told dr. Denman to go home while Cleo and Rikki just walked away.
Season 2: Cleo
This is not rocket science. The main villain of this season existed by the cause of the love triangle between Cleo, Lewis and Charlotte. Cleo was also the one who first discovered her advanced power and the first to control it. She is the first one to get attacked by Charlotte. In fact, she is the one who drives Charlotte insane to the point where she wants to take the trio's power; just for revenge!
Season 3: Rikki
This is just pointing out the obvious but Rikki is the one that season 3 is about. She is the only mermaid who has a obvious connection to the Moon Pool and the strange happenings. She is also the first one to get taken by the water tentacle. She is the first one to gain the water tentacle's trust.

So tell me: what is your opinion about this? Do you think it's just a coincidence? Sound off in a comment or comments below.