Progress update--the Forbidden Fruit anatomy page gave us the letter P (from はっぱ/happa/leaves), the last Japanese letter missing! I've updated
the font with this, alongside a hyphen (found in the forbidden fruit's right-hand text wall) and a more accurate letter S.
I decided to take a look at the fruit page itself, though the blotchiness and the how ancient the Japanese itself was styled (despite their using the English ゲート/gēto for "gate") meant I could only translate about half the contents and had to make a lot of guesswork, but here's what I ended up with--again, potential (though likely pretty minor by this point?) spoilers:
人界と魔界を積むぎりゲートのはぜまに
実りし果実口にし者は
世のここわりを見据えし知恵を受け
すべてを現象を統べる力を得る__禁断の
果実は長き時をかけ実ぞ乱をだれ
その未人の陰我より開きしゲートには未のはず乱れる
人界に封印されしゲートのうちに宿ると弛れる否。
禁断の果実口にし者その姿を見たものも居らず
実の容姿その実の味を知る者はいない。
その実古より伝承されし絵空事とくたえられる。
その実人界に伝わりし全地全ののうの神伝説
が起源とされてる出るつ人界と神界の双方のーーーち___
守護支配する王であり人界も神界も父を奪われる
出るつ た の 役目を有し____の異名で
全宇宙の気障を支配し_____ と呼ばれし武具を
有したその__神界最強の謳われし強大な力…
Those who eat the fruit that grows between the gates of the human world and the demon world will receive wisdom as they look ahead to the troubles of the world.
The forbidden fruit, from which one can obtaining the power to control all phenomena, ripens for a long time to bring about chaos. The fruit will be found when the gate is opened.
No one has ever seen the forbidden fruit, and no one knows what it looks like or how it tastes.
It has been handed down since ancient times and is considered to be a fairy tale. The tale of the God of all the earth has been passed to our world [oh hi That Toei Show], and the fruit is said to have originated from both the human world and the divine world.
When a king who protects and rules the human and divine worlds' father will be taken, he fulfills his role and is known as ____, who rules over all the troubles in the universe and is called ____. Whoever possesses the mighty [either "armor" or "weapon"] that is said to be the strongest in the divine world...
Pretty much the only story-relevant information appears to be the bit about someone losing their father, which is way more direct than the tablet last ep was. That suggests that Souma's a more integral part of Mutsugi's plan than just being an emotionally volatile knight. This may recontextualize the flashback itself--Mutsugi knew Godou had a son in training, so her whole reason for coming with him (or else her goal after her temptation) may have been to get him out of Souma's life at a crucial location in an attempt to kick-start the prophecy and force destiny onto her side. Come to think of it, nearly everything she's done after that is be very selective about who fulfills which parts of her goal for her, so attempting to do so with a prophecy wouldn't be out of character.
Those last missing words appear to have been smudged, very deliberately, to annoy me personally. But hey, I know more than I should now, so I'd consider it a win. I'm going to check what I can make of that portion of the Gate of Destruction page later, but some of the text from a cursory look seemed a little similar to what the stone tablet said.
Watching:
Kamen Rider Kuuga, Gotchard
Watched:
KR W, Gaim, Ghost - Build, Geats
Ultraman '66, Leo, Great, Nexus - U7X, Ginga - Blazar
Donbrothers
GS Sho, HwTM, Dogengers S1-4