I genuinely do not understand the reuse of the “we don’t recognize each other/thought each other were boys” childhood friends thing
Things that aren't as uncommon in real life as one may think:
+ mistaking boyish girls for boys and girlish boys for girls
+ parents dressing up very young kids in clothes of opposite sex for fun or simply reusing clothes of older siblings or relatives
+ children's appearance changing diametrically as they grow up
+ gender-neutral names and nicknames
+ not learning or not remembering names of people you've only interacted with in early childhood
+ getting separated from childhood friends because of parents relocating due to Japanese corpo belief of new experiences boosting productivity, and the culture of severing ties with people you won't be interacting with on a daily basis anymore (classmates, coworkers, neighbours)
That said, double gender confusion is indeed less plausible than only one person getting mistaken for a boy/girl.
Still, I just don't see why so many authors seem to think that "true" love can only be possible if they already knew each other as children and heavily lean into one side remaining obsessed with the other after not seeing them for ages in some stories.
Childhood friends are big in Japan because of het stories using them as a tool to inject friends of opposite sex for the protagonist, breaking through societal walls of limited non-romantic interactions with the opposite sex and hiding true feelings behind socially-acceptable masks (you get a character that's allowed to act friendly with the protagonist and already knows their truer-to-self side from their childhood). Romanticizing them there gives a side effect of yuri/yaoi authors exposed to it also finding the archetype romantic. Destined lovers or reuniting with loved ones is considered romantic worldwide. Childhood sweethearts may be seen as more pure/innocent and innocence is Japan's sex appeal. There may be bonus appeal of having a person that cares about you without having to deal with school courtship rituals, group dates or matchmaking. There's also manga industry wanting to be sustainable and pushing for tropes that sell, and it's fine as a reader to be fed up with consuming too much of the same thing.
My most loathed trope is getting caught out in the rain causes a character to become deathly ill from a cold, feverish, on death's door.
1) You don't get sick from the rain. Colds are caused by viruses. You only catch colds from other people.
2) If you have a fever, it ain't a cold. Colds are a mild irritant.
Getting soaked in the rain lowers body temperature, which weakens one's immune system. If you already have a weaker immune system, or weaken it with stress and overworking yourself (very common in Japan and in some other Asian countries), it's definitely possible for it to tip the scales and make you suddenly sick or even bedridden the next day. An average person is already exposed to people, viruses and other pathogens everyday, so getting infected is not a problem.
What exactly you're sick with / how you call it when informing others of your condition is not important if you're not seeking medical care, but a cold can be accompanied by (manga levels of) fever too and whether it's a mild irritant depends on the person.
The heat loss is the angle Japan uses in their rainy weather health advice. Usually accompanied by being told to rush home or other bathtub-equipped location, take off wet clothes, wash off the yucky rain water and plunge into a hot bath - or to not forget your umbrella in the first place.
