While visiting his hometown, junior high school student Michishio Nagasumi's life was changed forever when he nearly drowned. Though he was saved by a mermaid named San, there’s a catch -- her family is part of a merfolk mafia, and they abide by a strict rule: If a mermaid is discovered by a man, either he or the mermaid must die. That is, unless the man marries into the family! Faced with such a decision, Nagasumi can only oblige their customs and become a "happy" newlywed. Now, with a new school year around the corner, Nagasumi must find a way to deal with his new bride, keep her true nature a secret, and most importantly, escape inevitable death at the hands of San's over-protective father’s gang!
Raku Ichijo is an average high school student. He also happens to be the sole heir to the head of a Yakuza Family called the Shuei-gumi. 10 years ago, Raku made a promise… a secret promise with a girl he met. They promised one another that they will “get married when they reunite.” Since then, Raku never let go of the pendant the girl gave him.
Both of these school romances deal with a yakuza's daughter being suddenly forced into a relationship. The girl's family is so completely against it that they're constantly watching her new "lover," sometimes attempting to take his life in the process with hilarious results! To add to the list of people out for his life/against the relationship, there's a similarly overprotective assassin bodyguard yakuza in each too. Oh, and more than a single girl is smitten with the protagonist of course, one of whom's father belongs to the police - the natural enemy of the yakuza! While the plot in one versus the other is entirely different, if you liked what you've already seen, you don't have anything to lose by giving the other a try.
Yuuto Ayase is not interested in girls - if his two housemates are anything to go by, girls are loud, brazen slobs that are best left alone. However, when Yuuto accidentally discovers an important secret of his school’s most popular female, Haruka Nogizaka, the two become bound in a budding friendship. All too soon, Yuuto discovers that, despite her flawless appearance, Haruka is clumsy, naive, and a closet otaku... and he just might be falling for her.
Both are romantic comedies that has a litany of references to other animes. 'Seto no Hanayome' more often parodying, 'Nogizaka Haruka' moreso paying homage to various animes.
Often emotionally sickly sweet at times, they are fun watches that involves an average but 'honorable' guy meeting a girl from an incredibly well to do family (with highly capable body guards and overly protective dads).
Both girls are relatively air-headed, and both have a 'secret' that must be protected by the guy.
There's also a slight harem and love triangle feel to both, though with both not making it much of an issue.
Everyone around Kousaka seems to adore cats, but due to his allergies the teen can’t stand them. So when he wakes up one day and can hear what every feline is saying, Kousaka is annoyed to say the least. His new “gift,” it seems, is the result of accidentally breaking an enshrined statue of a cat; and what’s worse, Kousaka must atone for his sin and appease the vengeful spirit by aiding one hundred kitties-in-distress, or become a furry feline himself! Now, amidst helping various cats with mundane and trivial issues, Kousaka must try to dispel the jinx and attempt to salvage his self-respect – not to mention his love life - along the way.
Kei Kusanagi is a shy teenage boy with no romantic experience whatsoever... until he finds out that his hot new teacher is actually an alien! In order to conceal her identity, the two are forced into a pretend marriage... but is it really a pretense, or are they actually falling in love?
Both these series are romantic comedies starring a rather geeky kid who, through circumstances, are forced to marry a beautiful, kind and eager to please girl who's not quite human.
And in both of them, the couple is forced to keep their 'marriage' secret from all but a select group of people. And both couples soon find their relationship tested by other temptations as well as disapproving family-members.
So if you like one of these shows, I'd say there's a good chance of liking the other as well.
Ranma, raised to be a man among men, has a bit of a problem: he is half woman! While training in China he fell into a strange magic spring at Jusenkyo. Now, he is eternally cursed to change into a beautiful woman whenever he is hit by cold water, but that may be the least of his problems; his father has betrothed him to marry! There's never a dull day for Ranma as he attempts to find a cure for his curse, train to become stronger, and grapple with the fact that half of himself may be more feminine than his fiancée!
In both Ranma and Seto the male lead and the female lead are forced to get engaged and live together in the same house. Many more characters get introduced gradually and cause trouble for the two leads. They are both great anime for anyone who enjoys comedy.