Zju wrote: ↑Fri Jan 21, 2022 1:48 pm
The phonetic radicals aren't featural, but they mostly hint rhyme pronunciation, don't they? And it's the rhyme that those five similar looking katakana share.
It's a coincidence. Note that they're derived from the Kanji with little resemblance to each-other:
ウ (u):宇 (from the top part) "eaves" (MC */ɦɨo/, Middle Chinese */ɨo/ seems often borrowed into Japanese as */u/)
ク (ku):久 (from the left section) "long in duration" (MC */kɨu/; the character also has an on'yomi
kyû)
ス (su):須 (from the "feet") "mandatory, necessary; moment, short while" (MC */sɨo/, the later Kan'on reading is
shu)
ツ (tsu):川 (not a match) "river" (MC */t͡ɕʰiuᴇn/; a curious case, the on'yomi is normatively
sen)
ヌ (nu):奴 (from the right side radical) "servant" (MC */nuo/, the later Kan'on is, however,
do)
フ (fu):不 (from the side left of the downward vertical stroke) "not" (MC */pɨu(t)/, has on'yomi both
fu and
hochi, later Kan'on
fû, futsu, Kan'yō-on
bu)
ム (mu):牟 (from the top part, also not a match) "moo" (MC */mɨu/, the older Go'on is
mu however the Kan'on reading is
bō)
ユ (yu):由 (from part of the bottom, maybe a marginal match) "cause, reason" (MC */jɨu/, has Go'on
yu, Kan'on
yû, Kan'yō-on
yui)
ル (ru):流 (from the "feet" again, also not a match) "rapids, current" (MC */lɨu/; the Go'on
ru is now apparently less-common than the Kan'on
ryû)
ラ (ra):良 (from part of the top, different rime) "good, all right" (MC */lɨɐŋ/; Go'on
rō (historical
rau), Kan'on
ryō (historical
ryau); curiously, the Middle Chinese velar nasal seems to have been borrowed into Old Japanese as a glide or vowel, most usually some sort of */u~w/, but sometimes */i~j/; this coalesces with the preceding vowel to produce a long vowel in the modern language)
ワ (wa):和 (from part of the box, different rime) "peace, harmony" (MC */ɦuɑ/, Go'on
wa, Kan'on
ka, historical
kwa, Tō'on
o, historical
wo; also a part of the present Era name in Japan, 令和
Reiwa
ヲ (wo):乎 (from part of the top) "in, at,on" (not on the standard Jōyō list; MC */ɦuo/, Go'on
go or
o (historical
wo), Kan'on
ko)