The Demon King Who Lost His Job - Ch. 168

[MangaDex]

 

[R4nd0mGuy]

They are identical twin, right? Do identical twin have different blood types?

 

[Kjack49044]

They are identical twin, right? Do identical twin have different blood types?

I feel like it's a magical thing. The imprisoned sister is the rightful monarch, so her blood is needed to summon the spirit.

Also

Gyarados?

 

[LemonLies]

T

They are identical twin, right? Do identical twin have different blood types?

To answer your questions directly, I don't know if it's confirmed explicitly what kind of twins these two are. Fraternal twins can have different blood types, but identical twins share a blood type (except in a few very rare cases stemming from mutations). As the commenter before me stated though, I think this is operating by magic ritual rules and doesn't care about blood type per se.