Teppuu - Vol. 2 Ch. 5 - It's Square... Regardless of View Point, It's Square.

[MangaDex]

 

[Gyges]

What the fuck is this blood type shit?

 

[RyoSaeba]

@Gyges It's something very often depicted in mangas, in Japan they believe that certain traits in your character are linked to your blood type, in a similar way in western countries people believe your astrological sign (Zodiac sign) does.

https://en.wikipedia.org/wiki/Blood_type_personality_theory

 

[Gyges]

@RyoSaeba Do most people think its bullshit there too?

 

[RyoSaeba]

@Gyges Well, it is a pseudoscience so it's well-known for being bullshit, nothing new there. Still, like with zodiac signs and such you'll often find people believing in it on some level, it's pretty common afterall.
In mangas, authors usually do that to add more depth to the different characters in the story: you'll often see in extra/omake chapters some kind of "character info file" with their height/weight/birthday/zodiac sign/bloodtype/etc.

 

[Raymk]

@gyges yeah its pseudoscience and i'm sure some people believe it just like other myths.

 

[pacmanyo]

"I don't quite get what's going on, but it is fun!!" - perfect attitude