im not sure myself? it might come from the japanese spelling perhaps? i looked into it and found nothing, really.
episode 4 of season one was called MakiRinPana, if that helps.
*puts on hopefully helpful, only-partially-know-what-i’m-talking-about intermediate japanese student cap*
there is something in japanese i don’t know the proper name of, so i call it ‘letter families’. h, p and b are all part of the same ‘family’, which h being the ‘head’ of the family, so to speak. to understand what i’m talking about, have a look:
this is ha:
this is ba:
and this is pa:
it is the same with ‘ka’ and ‘ga’, if you google image them! but that’s beside the point right now.
anyway, when you combine two words in japanese into a single word, and the first letter of the second word is either a h or a k, you swap it out for the other member of its ‘family’. it’s actually most common to see h swapped for b. for example, ‘shooting star’, made up of ‘nagare(ru)’ (stream/flow) and ‘hoshi’ (star), becomes nagareboshi, and ‘flower arrangement’, made up of ‘ikeru’ (living) and ‘hana’ (flowers), becomes ikebana.
however, it’s not unheard of for h to be swapped out for p — though the only examples i can think of at the moment are for counters. a minute is ‘fun’ — one minute is ‘ippun.’ the counter for small animals is ‘hiki’ — one small animal is ‘ippiki’. so rin+hana combined into one word would be ‘rinbana’ or ‘rinpana’. of course, i’m no expert, but my theory would be is that panayo simply sounds sillier and cuter, so they went with that.
i think the real question is tho, WHY THE HELL DOES RIN CALL HER KAYO-CHIN
The two lines that turn は to ば are called dakuten and the cirlce in ぱ is called handakuten. Basically they change the sound of は which is considered ‘voiced’ to ‘unvoiced’ (or, sort of unvoiced in the case of the handakuten or ‘half dakuten’). The usage of dakuten here is part of something called Rendaku (somewhat easier guide here) that dictates when two kanji get stuck together to make a new word, the second one gets changed in pronounciation. Hanayo’s name is written 花陽 with the characters for ‘flower’ and ‘sun/sunlight’ (a super great name in my opinion, A+ to Hanayo’s parents for their taste). The character 花 gets rendaku’d 100% of the time. Serious, that character loves getting changed from voiced to unvoiced.
Rin’s name ends with ‘n’, no vowel sound, hence the general rule when applying rendaku where the preceding character ends with ‘n’ (or rather ん) is to use handakuten. (It’s related, to the best of my knowledge to a linguistic term called gemination.) Hence why the ship name is Rinpana. It makes sense in the minds of the Japanese, so much so that the fourth episode of Love Live season 1 is called ‘MakiRinPayo’ (well, really まきりんぱよ in hiragana as opposed to kanji but, hey, you get my point.)
As for the origins of Kayo-chin…
Kayo is an alternate character reading of Hanayo. The character 花 has multiple readings. Commonly, it’s just read as ‘hana’ but a reading specific to names is ‘ka’. Since Rin and Hanayo are childhood friends from grade school or something and name readings are tough enough when you’re an adult let alone when you’re still trying to learn common Joyo kanji I always assumed Rin just read it wrong and it kinda stuck. Alternate character readings are popular for nicknames anyway, or at least that’s the impression I’ve got after consuming so much anime (whoops.)
-chin is a childish mispronunciation and even more diminutive form of the more commonly known ‘-chan’ just to show ADORABLE CHILDHOOD BEST FRIENDS LOVE THEM FOREVER OH GOSH THEY’RE SO CUTE.
OH RIGHT DANG that’s why senpai is pronounced sempai!! you’d think my anime knowledge wouldn’t let me forget that one lmao… thanks for the super enriching japanese lesson! FINALLY THE MYSTERY OF KAYO-CHIN HAS BEEN SOLVED