In 1994, a promotional trailer was released showing an early build of Gensou Suikoden 1. Some notable differences are:

Interface:
• In Duels, your current HP are displayed as numbers, not as a bar.
• You don't see the HP of your enemy.
• The menu displaying your party's current HP during random encounters is different. It has a different frame (once, they show a fancy frame, and once a very plain one. Both are different from the final game). It also lacks the heart symbol in front of the HP.
• The number displaying the damage has a slightly different font.

Content:
• A duel with Barbarosa is shown.
• One monster is a color swap of the Strongarm. In the game, it has green skin, in this video, he looks human.
• Some monsters are shown which are not in the final build: a griffin, a soldier, minotaurs (?) and a knight.
• Enemies don't have an idle animation.
• Tengaar uses a spell which appears to not be in the final game.
• Some sprites are potentially different, but the video quality is low, so it's hard to discern.
• One random encounter uses a background with houses, which does not appear in the final game.
• A large number of characters have different portraits.
• It says there are 36 True Runes instead of 27 (Murayama himself said in one of the SRM interviews that they originally planned too make 36 but changed it to 27. It seems they decided on that pretty late in development.)

According to Raww Le Klueze, global admin of the Suikosource forums, there is a hidden marriage proposal spoken by The Castle Keeper zombie in Neclord's castle that can be found in the game's files in ve3.bin and ve6.bin. There is no known way to access it in-game. Translated to English, it reads:


It's unknown who Kazuko is or who wrote this proposal. This text is only believed to be present in the Japanese version of the game, with the North American version replacing it with a repeat of some past dialogue with the zombie before ending with the "Mwah!" replaced with a single "Yuk.".

According to Raww Le Klueze, global admin of the Suikosource forums, there is a secret 10th Old Book. There is no known button combination to access it, and acts more like a hidden programmer message with only one page. Translated to English, it reads:


Hideo Nomo was a Japanese baseball player and a starter in the 1995 Major League All-Stars game in the United States - the same year Suikoden was released in Japan - and is known as the first Japanese citizen to join an American major league team after having played professionally in Japanese major leagues.

After recruiting Hugo, you can give him your Old Books and read them in the Castle's library on the third floor. In the Japanese version of the game, while reading these books, dataminers years ago found that a seemingly unused crudely-drawn sketch of the game's cover artwork was loaded into the VRAM. In reality, this sketch was not unused, but was actually part of an obscure Easter egg: a secret 9th Old Book. While highlighting the 8th Old Book titled "The Kalekka Incident", press Square, Circle, Triangle, and Cross at the same time. This will unlock the hidden 9th volume entitled "Hirotaka Development Diary" (presumably referring to the game's producer Hirotaka Ishikawa). A very rough English translation of the book's first four pages can be seen below:


The last two pages of the developer diary featured the crude sketch of the game's cover art alongside a request to mail in your opinions on the game to a listed address that is presumably somewhere in Kanda-Jinbōchō in Tokyo (Note: this full page has not been translated). It's not known if this secret is in the Sega Saturn version of the game, but it is confirmed to work on the PlayStation Portable port, Genso Suikoden I & II. However, this port has the last two pages (including the sketch of the cover art and request for opinions) removed, reducing it to four pages instead of six.

During the introduction, several clips of the game are shown. One of these clips is of Flik, Odessa and Humphrey in a battle without the player, a situation that cannot be reproduced in the game.

Towards the start of the game is a scene in which the player must rescue Varkas and Sydonia while they are tied to posts, originally, in the Japanese release, the two are instead tied up to 2 crosses, resembling a process called crucifixion.

By reading Pahn's diary in the hero's home, it's possible to see his food diary. This is updated on the second day spent in Gregminster.

The name of Millia's dragon, Thrash, was originally Slash in the Japanese release.

"Barbarossa" was translated as "Red Beard" in the Italian localization, even though the character doesn't even have a beard.

Crowley is named after the real-life British mystic, Aleister Crowley.

Kamandol's final weapon upgrade, "Rod of Hermes", is a reference to the real-life caduceus, the "Staff of Hermes" used by numerous healthcare organizations as a symbol of medicine.

The hero was originally designed to wield a sword, but this was changed into a staff to give the game a more Chinese flair to it.

In Kurdish, Yuber's name means "shade", while his nemesis' name, Pesmerga, means "those who confront death".

Both Krin and Stallion will have an Escape Talisman with them when they first join your party, befitting their abilities and reputations. However, unlike the normal, single-use escape talisman items, these two specific talismans can be used an infinite number of times, as long as they are never stored in the storehouse. They have a special flag set that grants them this property, which is normally used for the Blinking Mirror. Because that flag is not normally used for escape talismans, it will be lost if they are stored in the storehouse. They can be transferred between characters without losing the infinite flag, however.

There are a number of interesting things about the bath. If you remain in the bath for a few minutes, your characters will turn red as though they're boiling hot. Milich, the very feminine general (though he is male), will sit in the women's side of the baths if you take an all male party. Fuma will be submerged in the water, with what appears to be a reed to breathe.

In the instruction manual, there is a character listed as Black Ears. This appears to be Kuromimi, based on the list of characters and their stars later in the manual, where Black Ears is listed as the Chitan Star.

An image in the instruction manual reveals that Georg Prime was in fact a member of the original Six Great Generals.

There are 3 unused rune Crystals in the game's code:
Shrike crystal: Permanently attached to Kasumi and cannot be removed or obtained otherwise.
Falcon crystal: Same as the Shrike crystal but attached to Valeria.
Flame crystal: Its description reads "Bell's rune". This rune cannot be attached to any characters, and Ronnie Bell already has her own unique rune, the "Hate Rune".

As weapon levels increase, they are also sometimes renamed. Many characters are recruited with weapons already upgraded beyond early level names for their weapons, but these names are still coded into the game.

Viewing these names, we see that Clive's weapons all have a wind theme (Wind, Storm, Tornado) and Warren's weapons are all references to the Norse God Odin, though badly mistranslated (Slavenil, Gunnigle, Odin).

In the game's opening scene, Barbarosa gives Teo his sword "Pluck" (mistranslated as "Prakk" in the English version). "Pluck" is a reference to JoJo's Bizarre Adventure, when Bruford gives his "Luck & Pluck" sword to Jonathan Joestar.