Note: This text sums up my findings I already shared across people and anonymous imageboards.

European manual mentions it on page 17 Here is a picture

American Manual mentions it on page 22 Here is a picture

I don't read Japanese to know if its in the Japanese manual. Here is a link to it and hopefully someone can confirm it. https://segaretro.org/images/6/6f/Thor2_sat_jp_manual.pdf

People have been mentioning this on gamefaqs since 2002. Here is a post by Chakan where he names the 7th spirit as Balu. https://gamefaqs.gamespot.com/saturn/197768-the-legend-of-oasis/faqs/5175

I managed to find the debug code for the Japanese version,previously not available on the internet. This will allow you to open the debug menu.

Action Replay code 160876B4 0100

Below is the comparison between the EU debug menu and Japanese debug menu.

I believe Chakan in his guide on gamefaqs made a honest mistake,due to CRT picture quality or something else I dont know. Thats an E not a B,so its not Balu but Ealu. If you enter codes to unlock all spirits and to have unlimited MP you can summon the spirit under the name of Ealu,and it is ARELE the one that is like a cloud.

In the file TH2.LOW found in any version of the game in the hex editor there is a very clear section showing this. Also in the picture below.

Maybe the manual refers to Koh and Tokipin as so called "spirits",but they admit they are not in fact spirits.

In the Item debug menu of the Japanese version you can drop an item looking like piece of paper.

If you pick it up there is text saying Japanese マッ プをーつ手に入れた English Translation I got a map (note:Translation was obtained using OCR)

Doe anyone know if its usable?

Also unsolved mysteries include the Small Robot in the house on the right at the start,the Pink Rat and that Reharl statue puzzle. Any info on any of thes things is appreciated.

Hey, sorry to necro this. I took a look at the Japanese manual and there is no mention of the 7th spirit there.

As for Earu, that is simply the romaji transcription of エアル, which the game translated as Airl. As far as I am aware, there is no 7th spirit and the English manual is lying.

Oh man this really bugged me back in the day! Hunting for skeletons and hoping for any kind of hint.

Could it possibly be that the translator for the game and the manual is the same person, or at least spoke to the manual translator, and mentioned it on the basis of redundant code left in? If you were just skim translating it possibly it could have made sense, and the translator thought they picked up on a secret they could let on for people to find.

A translator wouldn't have generally played the games so I don't know how else they would have thought of it. The UI graphics for example might not have been something they even looked at and wouldn't have known there was a lack of space for a 7th.