Kono Danshi, Ningyo Hiroimashita.

•both are pretty much the exact same scenrio, which i could not believe..... a merman being attended by a human school boy •both anime are different in type of format, where 1 of them is an OVA, while the other is like 3min per episode out of 13 series, which just sucks... •both anime are probably going to be similar and different in a way, new scenarios will emerge which the OVA doesnt show, while a strong bong between the merman and protagonist forms into something of love, or just plain friendship will be the same. •they are pretty much the same with a merman living in a container of water in the humans boys house.... and why is this not a 30min per episode series........ stupid 3min episode... read more 

Main characters are really similar. The mermen are basically the same, by looks and character. They both live in a bathtub in the house of a black haired high school boy. Kono Danshi series have unique style, and they're officially shounen ai, but Orenchi no Furo Jijou also has a shounen ai feeling to it, despite not being of the genre. Orenchi no Furo Jijou has more more characters and more happenings. 

Basically the same plot. A boy finds a merman and brings it home where it ends up living in his bathtub. Both kind of hint at Shonen Ai as well. 

Similarities: -High school boy finds merman -The character designs look very similar -Both short and sweet -Both have manservice -Both are very cute shows Differences: -Orenchi no Furo Jijou is more lighthearted and Kono Dashi Ningyo Hiromashita is more dramatic -Kono Dashi Ningyo Hiromashita is more shounen ai (Boys' love) -Orenchi no Furo Jijou has more characters -Kono Dashi is jus one OVA but Orenchi no Furo Jijou has 12 five minute episodes 

both are short, fruity, and about a boy who keeps a merman in his house.  

-Both MC's are high school boy. -Both MC's have black hair. -Both MC's finds a merman. -Both merman live in a bathtub in the house of the MC. -Both series have similar character design. Basically, it's the same story. A black haired high school boy finds a merman and takes the merman in his house. Then offers the merman a bathtub as a refuge .That's the story . . 

A boy finds a merman and he takes the merman home. It’s kinda the same story but in a different font lol  

Both have a protagonist that took in a merman to live in their bath tub. Both focus on the close bond between the protagonist and the merman despite the fact each character came from different worlds. The only difference is one is a BL while the other just has an implied relationship. 

Mid-length OVAs. Dreamy atmosphere. Beautiful, stylized animation. A bit of drama but mostly cuteness. A romance that doesn't just repeat shounen ai clichés. Deal with one main character being scared of letting people close and how the other one's love changes that. The main difference is that Kono Danshi, Ningyo Hiroimashita is fantasy while Doukyuusei takes place in a school.