Is there an Anime Girl Type that is equivalent to the standard American romantic comedy heroine?

Manic Pixie Dream Girl? Not really anime type, but that's the trope that most earlier rom-coms played off.

Oh, and could you explain the thing about typing by functions?

MBTI actually has a foundation of 4 different functions, which are oriented either externally or internally. With each type referring to a unique configuration in terms of order (dominance) and orientation. Each type has: Thinking, Feeling, Sensing, and Intuition. Thinking/Feeling are judging functions, and Sensing/Intuition are perceiving functions. And all four are either extroverted or introverted.

For an ISTP, the function stack is: Dominant Introverted Thinking, Auxiliary Extroverted Sensing, Tertiary Introverted Intuition, Inferior Extroverted Feeling.

To type by function would mean to figure out what functions you use, and which are dominant, and then determine which type correlates to that stack.

Each type has one of each and no duplicates, go in an EIEI or IEIE pattern, and are either JPPJ or PJJP. Each function can be abbreviated to a two letter pair. ISTP would be: Ti-Se-Ni-Fe.

Judging functions being how you make decisions, perceiving functions being how you receive and examine information (more or less. It gets a bit more complicated than that).

So if you have TI, you also have Fe. Or Te/Fi. Then you have Se/Ni or Si/Ne. Your judging and perceiving functions are 'linked' so to speak. if one judging function is introverted, the other is extroverted. And same goes for perceiving.

The I/E in your type refers to your first dominant function (for ISTP this is Ti). P/J refers to whether your first most dominant extroverted function is judging or perceiving (for ISTP this is Se - perceiving). S and T both refer to your top two functions, one is your dominant perceiving function and the other is your dominant judging function (for ISTP this is Se and Ti).

With those four letters, you should know your dominant and auxiliary function. And the tertiary and inferior functions can then be deduced. Since we have Ti-Se for ISTP, tertiary is Ni (to pair up with auxiliary Se), and inferior is Fe (to pair up with dominant Ti).

ISTPs, following the functions, have an internal logical model of how to decide and think about things, and take in concrete external information about the world.

But yea, typing by function is what it sounds like, figuring out the functions you use, and then determining what type that is. As opposed to just going "I/E is about whether you are extroverted/introverted". Or going by descriptions of types.