Bombay!
Well what do you know... there's something to be learned from watching anime after all! (Or perhaps it's just me, a little ignorant.)
I started watching Yakitate!! Japan again recently and a certain episode made me wonder... whether the blood group 'Bombay' actually exists. After all this is Yakitate!! Japan, the show where puns and parodies are the order of the day. Not to mention outrageous reactions.
So I turned to my trusty knowledge source - Wikipedia (heh) - and discovered this blood group exists and everything said about it in the show was true.
The blood type Bombay is rare (3 thousand out of 6 billion type rare) and its defining characteristic (well for us non-geneticists) is the fact that people with Bombay blood cannot receive any other blood type. Not even O negative. However! Any A, B blood type is compatible with it (kinda sucks eh).
Making matters worse, most hospitals would not even think of testing for this type and would conclude an individual must belong in the blood group O (as O negative types also can't receive other blood types). Categorising Bombay blood types in this manner is dangerous, given the risk for adverse reactions if an incompatible blood type were injected into an invidivual.
For an individual to have this blood type, both parents must also have the same blood type. Because of this, members of isolated communities and royal families have a higher chance of carrying this blood type. (Inbreeding, hmm.)
I feel like a 324-layer croissant, or a 5-layer rye bread, or a sushi style melon bread, or a crown shaped pandoro encrusted with fruit soaked in honey.
Oh, individuals with blood type Bombay needing a transfusion have almost no hope, especially those involved in an accident, as it's unlikely blood banks store it. Surgical patients opt to store their own blood prior to an operation.