To be fair, Pokémon is abbreviated English, while pachinko is recent from pachin, the onomatopoeia of the loud sound made by the metal balls.

I believe the change into “h” sounds is more applied to words that were traditionally initiated in “p” but morphed over time, in turn also making words starting on “p” an oddity.

This is an interesting phenomenon in language change. There is the question of what sounds are legal in the language (or what sound combinations, and in what contexts), and there's the separate question of which of those possibilities actually exist. For example, syllable-initial "th" is never followed by L in English, but the sound sequence generally doesn't pose difficulties to English speakers, who are already familiar with words like e.g. "three", "shrink", and "sleep".

For a sound to occur in a language, there are two requirements:

The obvious one is that it has to be possible.

But the less-obvious one is that its precursor in the ancestral language must have been possible there. This is what causes strange gaps where it looks like a sound should be possible, and yet it never occurs.

Fair; though I didn't say it's impossible, just unlikely :)

Japanese words starting with "p" still exist, but they tend to be loanwords (pokemon = pocket + monster) or onomatopoeia (pachinko = pachin + ko). Thinking of it now, pokapoka is also a word, but again, an onomatopoeia.

I thought of Pocky, but turns out this is an onomatopoeia too

> It was named after the Japanese onomatopoeic word pokkiri (ポッキリ), which is supposed to resemble the sound of the snack being cracked.

https://en.m.wikipedia.org/wiki/Pocky

What about パクリ? and ぽっかり?

Those belong to the "onomatopoeic" stratum; you can form e.g. ぱくり・ぱっくり・ぱくぱく・ぱくっと.

Poka-yoke

those are imported words.

There are also many native Japanese onomatopoeiae using an initial p sound. Interestingly enough, if we're at Pokémon, Pikachu's name is influenced by the onomatopoeia /pikapika/ which means to shine, sparkle or flash. But if we look at the original pronounciation of the Japanese verb 光る/hikaru ("to shine"), it would have been pronounced /pikaru/ in Old Japanese, so it looks like the onomatopoeia has re-established itself.

The same is probably true for the Japanese word for flag, 旗/hata - it would have been pronounced /pata/ which is suspiciously reminiscent of the onomatopoeia /patapata/, often used for thin pieces of material flapping in the wind.

The Pikachu name is also partly derived from the pika, a small rabbit-like mammal native to Asia and North America.

The pika is an obscure (yet barely interesting...) rabbit thing with no cultural salience, whose most noted features are its alarm call and lack of visible tail, nor are its names pronounced much like the pika in Pikachu in the languages Japanese has much exchange with. Pikachu is explicitly a rodent (a "mouse" with some squirrel inspirations) designed in the early 90s with none of those features.

This claim seems profoundly unlikely.