Romance can be one of the most thrilling parts of the anime viewing experience - unless you hate the canon pairings.
Some of the worst anime relationships are explicitly abusive, like the marriage between Rei and Enji Todoroki in My Hero Academia - the series doesn't try to present it as loving, and the fans are unlikely to see it that way either. But not all terrible anime couples are treated with such nuance. Despite spending the majority of their time on-screen fighting, the eventual union between Keitaro and Naru in Love Hina is supposed to be romantic. Worse, so is the pederastic relationship between teenage Ren and his legal guardian Haru Kaidou in Super Lovers.
What makes a relationship awful is subjective, so it's possible a couple you're rooting for bothers other people. If that's the case, it's time to take a glimpse into why others may not feel the same way.
Enji and Rei Todoroki's relationship primarily exists in the nightmares of their children. They don't marry for love, but because Enji needs someone with a quirk he can combine with his own to produce a child that would surpass his superhero rival, All Might.
When Enji starts acting abusively toward their four children, Rei attempts to protect them, only to be physically assaulted for her efforts. Years of abuse impact Rei's mental stability, and she ends up splashing boiling water on her youngest son's face because he looks so much like her husband.
Enji objects to her outburst, unable to recognize his role in the event. Instead, he decides Rei is simply "insane" and needs to be locked up in a mental institution for the rest of her natural life. Meanwhile, he carries on abusing the kids.
When the series begins, the two of them are technically still married, but the union is clearly a loveless one. At least the series isn't trying to sell it as something positive?
An illegal age difference is pretty much an instant deal-breaker in terms of a relationship's quality, which is why Rin Kokonoe and Daisuke Aoki do not belong together. They first meet when Rin, a third grader, is a student in 23-year-old Daisuke's class. Rin disrupts class with sexually explicit comments toward Daisuke.
At first, Daisuke is flustered and confused - a totally normal reaction to a seven-year-old coming on to you! Rin's behavior stems from a troubled home life, but rather than referring her to a counselor, Daisuke ends up reciprocating her romantic feelings.
The relationship isn't made official until Rin's 16th birthday. That doesn't change the fact Daisuke wanted to be with her when she was a little girl. Also, an adult dating a 16-year-old isn't exactly great, to say the least.
When two mass murderers decide to date, it's probably not going to result in a beautiful relationship. Misa Amane is obsessed with Light Yagami to the point where she'd gladly die for his sake, and Light is more than willing to let her die if it's to his benefit. Light sees Misa as an object he can manipulate to achieve his murderous ends, while Misa sees Light as an otherworldly savior.
It's an unequal and abusive relationship, especially when Light knows he's the serial killer Kira. During the part where he forgets who he is, Misa is clingy, jealous, and demanding - behavior Light passively accepts.
There isn't a single moment in all of Death Note where the two of them genuinely connect as a couple. Sure, few people are watching this show for the romance, but it could have been better than this.
Mikagi and Ceres begin their relationship on good terms, but when Ceres - a goddess - grants her husband godlike powers, he becomes unhinged and uses the power to try and take over neighboring villages. He also tosses Ceres's ceremonial robes - which she needs to ascend to heaven - into the ocean, and also kills their firstborn child. Ceres then tries to kill him, but even that doesn't end things - since Ceres doesn't have the robes, she continuously reincarnates as a member of each new generation of her family - and Mikagi does the same.
Ceres and Mikagi eventually end up as spirits possessing a twin brother and sister, Aki and Aya, who are the products of their bloodline. Mikagi uses the boy's body to pursue Ceres, who is inhabiting the girl's body. He attempts to kill and assault her, and he is only stopped when the boy sacrifices his own life to get rid of him.
When Mikagi finally dies, he's reunited with Ceres in heaven. Stripped of his powers, he's suddenly apologetic and claims to love her - a feeling she reciprocates. The series ends on that maudlin note, sending the message that centuries of abuse is totally cool as long as you're sorry afterward.