While in E.V.O. Search for Eden, the Sun God's gender is unknown until Gaia refers to him as male in her own intro by calling him her father, 64 Okunen Monogatari directly adresses him as a male in the intro when he names her.
The latter reference is strangely missing in E.V.O. Search for Eden, despite the translation being rather accurate otherwise.
The Sun God's role
In E.V.O. Search for Eden, the Sun God only appears in his own introduction after booting up the game.
The introduction shows him teaching Gaia about the "Survival of the Fittest" and the protagonist's role shortly after she has been born.
After this cutscene, the Sun God is never seen again and does not partake in any other actions over the course of the game, but is occassionally mentioned by Gaia, who directly continues to refer to him as her father.
His full cutscene can be viewed in the gallery below.
Gallery (Sun God's introduction)
About 4.6 billon years ago, the "Sun" had nine smaller stars and named the third one "Gaia"
The Sun: "My dear, Gaia! Please listen to me.
From this time forward, every 1 billion years, you will have children...
... called "Life". One of them will be able to help you to...
... build a new era.
Each child must endure a difficult trial. You might think it's...
... too severe, but it is necessary.
The trial is a test of Nature: "The survival of the fittest".
If he passes, I will allow him to be your partner and to enter...
In the Japanese version of the Sun God's introduction, any creature, that overcomes the ordeal of the survival of the fittest and becomes a god is allowed to become Gaia's partner and meet Gaia and the Sun God in Eden.
In the English version, this was changed, so the protagonist is no longer referred to as a being of ambigious gender, but a male. The original work never states the protagonist's gender.
This later results in quite an oddity when the presumably "male" protagonist can evolve into a female mermaid in one of the final chapter's stages, but also become a male human. As for any other species, the protagonist can be male or female at will. (for example, they can be a lion with or without a mane)
Also, the protagonist no longer becomes a god and they are now the only lifeform chosen as Gaia's partner instead of everyone being capable to become Gaia's partner, if they survive the ordeal.
With the Japanese original's intro, Bolbox's attempt to become Gaia's partner also makes more sense than in the English version, as he now has a reason for it instead of simply being some creature trying to enter Eden without being the chosen one.