It's mildly amusing at times, but not as funny as I'd expected. Only a weak recommendation, at best.
Tatsumi is a high school student with a merman called Wakasa living in his bathtub. Wakasa is a blonde, sensitive blushing maiden of a man, with amazing hair and no clothes. (Completely chaste, mind you. He's clingy, dependent and all over Tatsumi, but nothing gay is going to happen even when the two of them are having a bath together.) Sometimes he's like an insecure housewife. Sometimes he's like a big goofy child, without a thought in his head except a desire to play.
He also has friends who'll similarly be showing up for naked happy bath fun play times, all male and almost as pretty as he is. They're all seafood too, obviously. There's an octopus, a jellyfish and a hermit crab.
Could this series, mayhap, be aimed at girls? (It's a reliable anime principle. Unless a show's target audience is of primary school age or below, then a cast full of girls will indicate that it's aimed at a male audience and vice-versa. This becomes an ironclad law if everyone's a gorgeous, shirtless drama queen.) Anyway, let me look it up. The original 4-panel gag manga was published in Monthly Comic Gene, a shounen (boys' manga) magazine for female readers. No, really. I'll explain. Boys' manga used to involve action and fighting while girls' manga would be full of hearts and flowers, but these days the gender demarcations have blurred. Girls read Shounen Jump and so on. We thus have magazines like Monthly Comic Gene, although that information has nothing to do with this show.
Tatsumi is the straight man. He keeps his guard up and rarely shows much personality, although he ends up being quite nurturing towards Wakasa. They're like a husband and a housebound wife. Wakasa is of course a great big girl's blouse.
Of the supporting characters, Takasu is a swaggering, rough-talking octopus-man whose tentacles can do anything. This includes heavily erotic massages. Mikuni is an airhead jellyfish who's transparent and can administer electric shocks. The funniest one, though, is Maki the hermit crab, who unlike the others is only the size of a real hermit crab and is desperately negative about everything.
Tatsumi also has a little sister, who likes her brother a lot and sees all these pretty boys as rivals. She's very aware of the gay readings. She's somewhat amusing too, with the squick factor ameliorated by her age. She's tiny. She must be, what, six? Even in anime, that's too young for anyone to take her ambitions seriously.
I have no problem with this show being for women, or with the fact that it's about shirtless pretty boys having homoerotic subtext instead of a plot. It's just not that special. It's okay. I watched it. However I'm not entirely sure why and the answer is probably in large part "because each episode is only four minutes". There's mild amusement to be had from all the ways in which the show plays to the gallery, e.g. the "nearly but not quite" point at which chiselled male nudity becomes safe seafood. Even the boys' names have gender-ambiguous endings (-mi, -sa). The only gruff, manly voice in the show belongs to the rubber duck when he occasionally talks for comedy value in the closing credits.
It's pleasant and inoffensive, though, while I like the character development it gives Wakasa and Tatsumi. It's a chaste romance, effectively. It's quite nice, in its way, even if after finishing it you might be wondering why you bothered.
"Suddenly meeting your girlfriend is too much for me."