i will now explain why iwaoi are soulmates using actual real life psychology concepts (this is me making studying more fun)
1) the mere exposure effect
this states that people tend to have a preference for those we are around most often. that's why people tend to become friends and develop crushes on people that they spend a lot of time with for school or work.
we can apply this to iwaoi because they've been best friends since childhood, playing for the same teams and having the same classes. they spend a LOT of time together.
2) reciprocity
we tend to like people who like us. that's why one-sided crushes often develop into something mutual.
this means that if the mere exposure effect didn't cause both iwa and oikawa to be romantically attracted to each other (it would most likely cause at least one of them to catch feels), the other would probably reciprocate the feelings eventually.
3) sternberg's triarchic theory of love
sternberg believed that the "perfect relationship" would have passion(infatuation), intimacy(liking), and commitment
look me in the eye and tell me iwaoi doesn't have commitment. i dare u. intimacy is also obvious because they genuinely like being around each other. the most arguable (and least canon) one is passion.
the definition of passion is "strong and barely controllable emotion." and the definition of infatuation is "an intense but short-lived passion or admiration for someone or something."
iwa canonically admires oikawa, and oikawa most likely reciprocates these feelings based on the clear level of respect and understanding they have for each other.
in conclusion: iwaoi canon
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