Japanese language never lost /p/ completely.
In second half of 10th century, change /p/ → /w/ occurred intervocalically, except (1) in words seen as transparent compounds (e.g. modern asahi, mohaya), (2) morpheme-initially in Sino-Japanese words.
During Late Middle Japanese, change /p/ → /ɸ/ occurred word-initially and intervocalically (in words not affected by previous change and in words newly created since previous change), except in some mimetics.
Intervocalically means that this change did not occur after /N/ or /Q/.
Bjarke Frellesvig (2010, "A History of the Japanese Language", pages 313-314) (with corrected parentheses):
11.3.1 Retention of /p/ after /Q/
Just like the change of internal /-p-/ > /-w-/ in EMJ did not apply to /-p-/ after /Q/ (7.3.1.2), the change of /p/ > /f/ did not apply to /p/ after /Q/, thus leaving -pp- (= /Qp/) sequences in addition to appare 'splendid' and moppara 'entirely' mentioned in (7.3.1.2), for example yappari (not in Vocabulario) /yaQpari/ 'as expected, sure enough' (thought to be related to the root yapa- 'soft, pliant' which also has reflexes in yawa-; yappari today has the variant yahari which is a hypercorrect back formation, probably based on the spelling やはり), yoppodo /yoQpodo/ 'very, much' ((?< yopodo) < yoki podo 'good extent'; is today used mainly in the shape yohodo which like yahari is a hypercorrect back formation), or cappato /kappa-to/ 'suddenly'.
By far the most occurrences of /Qp/ are found in SJ vocabulary where retention of /p/ after /Q/ has been analogically extended so that all SJ morphs with initial NJ /h-/ (< LMJ /f/ < EMJ /p/) have automatic allomorphs in /-p-/, if they are used after /Q/. Similar lexical alternations are also found, although to a lesser extent, in the native vocabulary when prefixes of the shape CVQ- combine with forms with initial LMJ /f-/, e.g. (13) with intensifying maQ-:
(13)
| maQ- + |
|
| fadaca 'naked' |
mappadaca 'stark naked' |
| fajime /fazime/ 'beginning' |
mappajime 'origin, start' |
| fira 'flat' |
mappira 'without fail' |
| firu 'daytime' |
mappiru 'middle of the day' |
| fucura 'core' |
mappucura 'core' |
There are other verbal prefixes of the shape CVQ-, e.g. EMJ piki- 'pull.INF' > piC- > LMJ fiC- > NJ hiQ- after which verbs with initial /h/ appear with /p/ (e.g. LMJ fippar- 'pull, drag' > NJ hippar-). All such forms may now be regarded as lexicalized and some may have been formed analogically, but the point remains that they reflect preservation of /p/ after /Q/. This is also the case with a small number of compounds which have second components with initial /pp/, alternating with initial NJ /h/, e.g. LMJ asafara 'morning-belly; stomach of someone who has not eaten breakfast' > NJ asahara ~ asa-ppara (not attested until the eighteenth century), the reduplicated form NJ happa 'leaf' (childish) <= ha 'leaf'(< OJ pa), or a few NJ forms which are compounds with de- 'protrude' (e.g. deppa 'buck tooth' (ha 'tooth'), deppana 'long nose' (hana 'nose')).
11.3.2 Retention of /p/ after /N/
In EMJ, /p/ was neutralized as /b/ after /N/ by the postnasal neutralization rule, i.e. ///Np/// => /Nb/ (7.1.2.2), but as discussed above (11.1.1) this rule was lost in the course of LMJ. As after /Q/, /p/ was preserved after /N/ and did not change to /f/, and from LMJ onwards /Np/ became a frequent sequence, as in the few examples in (14) from Vocabulario. Most words in this group are SJ, as in (14a), but a few examples are also found which include native vocabulary, see (14b):
(14)
a. anpu 'safety' (安否), bonpon 'book from India' (梵本), monpa 'sect' (門派).
b. binpigue /binpige/ 'hair and beard at the temples' (bin 'temple' + pige 'beard'), bimpima /binpima/ 'right moment' ~ bin fima (bin 便 'convenient' + pima 'time, moment')
Compounds such as SJ xinfôracu (神法楽) 'entertainment for the gods/spirits', which is one of the few words with the /Nf/ in Vocabulario, is a transparent productive compound from <= sin 'god/spirit' + fooraku 'entertainment'. On the whole, words with /Np/ must have been lexicalized after the loss of postnasal neutralization, but before /p/ > /f/ (or have been analogically formed). Words such as those in (14) which retain /p/ after /N/ contrast with words such as sanbô and nanbocu in (3) above which have /p/ reflected as /b/ after /N/ and must have been lexicalized before the loss of postnasal neutralization.
In Portuguese sources about Japanese from 16th / 17th century, "ǒ" means /ɔː/ and "ô" means /oː/.
