Gameplay Idea:

This faction abhors violence and conflict with other sentients and prefers to focus on finding the perfect way to guarantee a peaceful relationship with neighbor factions, as such they start off with unlocked diplomatic options/tech that facilitates these initial peaceful negotiations. Their narrative and gameplay path revolves around achieving a peaceful and harmonious coexistence with other races, unlocking faction specific techs later on to better facilitate this and opening quest-lines (perhaps with some minor deviations and surprises if possible) specific to each faction in order to unlock an exclusive diplomatic state, called ''In Harmonious Concert'' as a placeholder or maybe definitive, in order to achieve a state of Sublime Symphony as a faction specific diplomatic victory condition (as a substitute or additional option to the already available diplomatic victory condition). 

As for Empire-Wide effects, the establishment of a stable and peaceful relationship with minor factions provides additional bonuses to Food and Production as a means of supplementing their internal focus of Science and Influence with and increasing Dust income as a result of a bonus for a wider relationship network with both minor and major factions (a result of the trade boom that peace provides). 

Climbing up the diplomatic progression ladder with major factions provides bonuses with all FIDSI as their more elevated status justifies this race's ability to increase their output as a civilization, along with the singular rewards given when pursuing the faction-specific quests described above. A small and timed happiness bonus comes as a reward for the actions described before hand with an ever increasing long-lasting happiness bonus awarded when expanding the wider relationship network described beforehand.

 Since their goal in life is to promote peace and adhere to pacifism, their fleets would focus on engaging ships with sonic weaponry that disables enemy fleets, conducting defensive operations and never offensive ones. The Nereid Fleet's mission statement is one of diplomacy, charity and guardianship. The effectiveness of said sonic weaponry is increased with the use of heroes and tech upgrades. Heroes may also be used to facilitate diplomatic actions through faction-specific progression trees.

Biography:

The Neradians are an aquatic people hailing for the sapphire planet of Egea. Their history and legacy has taught them that war and conflict is a pointless and ultimately fruitless endeavor, as their were enlightened by a messianic figure through the art form of music, leading to a species-wide epiphany of their own singular gift of promoting peace and enlightenment with said art form. As such their leaders and representatives are all accomplished musicians, the most highly praised having the greatest aptitude for composition and the talent to express said work, with their captains and emissaries initiating first contact with either their own singing or conducting an orchestra. In their study of themselves and their music, they came upon the purpose of discovering the perfect symphony to bridge any possible gap or divide between races, witch they claim as their greatest accomplishment and celebrate whenever such a piece of art is created. Whenever faced with a military situation, they prefere to rely on their highly advanced sonic weaponry to disable their opponents and protect those they establish diplomatic ties with. Their ultimate goal is to achieve a galaxy wide state of peace witch they have dubbed the Sublime Symphony.

Cool ideas here. I like their non-leathal weaponry themes. I'm curious how that would work in-game? Sounds fun. Good luck!