Baädaka

Origins
Baädaka is an area inhabited by the Neen, and includes a deep, freshwater lake connected via river to an ocean bay (mixed fresh/salt water), as well as some surrounding land (partially used on the surface; partially underground/underwater caves). The only visible above-ground indications of civilization are some poorly-maintained buildings (factories/workshops) and some concrete "stacks" poking out of the water. At night, there may be lights/glow visible far beneath the water's surface.
Baädaka comprises around a dozen underwater settlements of varying size, loosely organized under a single banner in order to present a united front against land-dwellers who once fished, dumped rubbish, harvested from and generally wreaked havoc on the underwater world the Neen called home. Neen liaisons/ambassadors work to maintain good relationships with nearby land-dwellers and/or those who pass near or through their waters, and they sometimes help with maintenance of trade/fishing routes, resource handling/harvesting, marine defenses (against storms, invasions, marine beasts), etc.
Government
Neen government is a loosely-organized network of settlement leaders, which varies depending on the settlement in question. While villages generally appoint or accept the strongest among them as representative, larger cities hold primitive elections (winners are more often decided based on fighting/singing abilities than they are on any candidate's politics). As the Neen have long existed in solitude - few even know their own families - any governmental structure is relatively new to them, and therefore may appear primitive/chaotic/weak to those who have long understood political/social hierarchies.
Culture
The elder Neen would see their interactions with land-dwellers end at the necessary "niceties" - especially given new technological advances that may pose a threat to the Neen's way of life. They typically find land-dwellers to be loud and dirty; most Neen are ungainly on land (read: terrible combatants) and they prefer the quiet of the ocean. However, the younger generations find many new land inventions intriguing and exciting - especially their uses for electricity - and they are at the forefront of the Neen's technological revolution.
The Neen have always been craftspeople, and young Neen scientists and entrepreneurs have begun using simple steam, current and pressure-powered generators to create and store electricity. That electricity powers machines to help fabricate tools, materials and small parts. Many Neen also have the ability to generate short pulses of electricity through their bodies, which allows them to test (and ruin!) small components.
Aside from keeping themselves safe and learning new things, the Neen have no particular interest in trade with land-dwellers, as few land implements are useful underwater, and vice-versa. Furthermore, the Neen have no interest in land currencies (though they will plunder sunken ships). They are not interested in expansion (or, perhaps they are not yet organized enough?). Mostly for these reasons, they have no military to speak of, but will work together to fend off threats when necessary.
Most Neen inventions are created purely for fun/entertainment/beauty, and they are especially interested in instruments and other items related to music. Their heritage/stories/knowledge are generally passed via song, and they are largely performers/artists. This has largely influenced (or was influenced by) their language, which is a combination of mouth-sounds, telepathic empathy (ability to understand/project emotions) and sign language (expressions and hand motions). This method of communication is both blessing and bane; while the Neen are easily able to understand one another and to understand a person's emotions, they are terrible liars and rarely understand language nuances such as sarcasm.
They enjoy both giving and receiving gifts, the most popular of which are necklaces (usually crafted from "found objects", always crafted by the giver). To receive Neen jewelry should be considered an honour by any land-dwellers, as it marks the receiver as a trusted friend.
[Original Source: Claim post by /u/madicienne on October 27, 2016]