creation
Every time a planet or star gets born, so does a Lunieve. Their heart is made out of the same core as the planet or shines the same light as their star, binding them to this celestial body forever. The lifespans are connected as well; a Lunieve can only die once their home dies as well, and they cannot be killed by any other means except getting their core directly removed.
The book they carry with them at all times has the entire history as well as future of their home written inside, although the future reveals itself once that time has passed and cannot be read before.
society
Lunieves are a very sociable and kind race, usually almost always making friends with different races on their travels. Oftentimes they pick up quirks as well as collectables from others which they will carry with them, usually directly in their core window. They have a good memory, which is why they usually never forget a friend they have met. Of course, as they are very impressionable, it can sometimes happen that they trust the wrong people and fall victim to their actions and experiments.
As Lunieves are a species that takes a lot of pride in their collections, whenever a Lunieve falls in love with another one, they will give them their biggest planet or brightest star as a form of endearment.
While they are herbivores, they have the ability to eat meteorites and asteroids too, although just in small quantities. Some types of celestial bodies can be seen as delicacies and are the favorite snack of many.
locations
As Lunieves are an always traveling species, they rarely settle down and call a place their home. While this is the case, there are a handful of places for everyone to visit.
The Library
The Library is a huge, hollowed out planet, in which every book of every deceased Lunieve is stored. Inside, the Library is grand and mostly made out of mahogany with silver decorations, storing multiple thousands of books to date, inviting every person of every race to come visit and read through the past lives of their society as to honor their memories. Once a lonely book gets found in space, it is customary to bring it into the Library, where it gets verified as Lunieve book or just some lost one. In some rare cases it can happen that a past friend of the deceased Lunieve carries their book with them until their own passing, as to always keep their friend close by.
Central Station
A huge spaceship-like station was built in the middle of the universe for every Lunieve to make friends of their own kind of or to regroup with their friends. As many Lunieves choose to travel alone, it can be a nice change of pace to make friends of their own kin and possibly to exchange knowledge or souvenirs.
In the heart of the Central Station is a huge bulletin board on which every race in the universe can post their requests or rumors on. As some Lunieves prefer to explore the universe by fulfilling requests or finding treasure, others prefer to simply meet new people to learn about them. The Central Station is also a place where every Lunieve can trade or sell their souvenirs with each other, potentially earning them rare currencies to buy more things with.