If you're looking for anime similar to Tropical-Rouge! Precure Petit Tobikome! Collaboration ♡ Dance Party!, you might like these titles.
Mako is a young siren and daughter to the King of the Sea. In a stormy day she rescues the young sporto Akira from a wrecked ship, but ends up fallign in love with him. So, with help from the Witch of the Sea, she's transformed into a human, and becomes a highschool student who helps everyone with her strong sense of love and justice and her magical pendant, the "Tear of the Mermaid"...
After a powerful foe met his end, Kaito and Lucia were finally reunited; but they don't live happily ever after. Though he promises to return to Lucia someday, Kaito decides to go to Hawaii, become a better surfer, and try to find himself again; but along the way, an accident causes him to lose his memory and he ultimately falls in love with another woman. In the mermaid world, things fare just as poorly: with Sara gone, a new mermaid named Seira has taken her place and constantly shows up in Lucia's dreams, warning her about troubles that lie ahead. As if things couldn’t possibly get worse, a new powerful villain named Mikeru has appeared; not even the strongest mermaid song can harm him! Can Lucia get back the one she loves and defeat her enemies?
It's summer vacation, and Lalabel and Teko have different ideas of where they should go; Lalabel wishes to go to the sea, while Teko wants to go to the mountains. After a game of rock-paper-scissors decides on the ocean, the girls travel with Toko to a guesthouse of her aunt and uncle. However, there's a problem – the adults are away, and the couple's son Ryota is left to tend to the guests himself! Luckily, Lalabel and the girls are more than happy to help with the work, even though the nefarious Biscus has set up his own magical inn nearby...