"The Dasein," was and maybe still is, the object to be defined by existentialist thinkers. It dominated the period up to whenever it was the sciences made such inroads into consciousness that thinking about consciousness could no longer remain independent of science without beginning to sound like an utterance from a religious nut. "The Dasein" is an attempt to arrange words around an objectiveness which mathematicians would have been proud of. And if you think of it as "The Dasein" you might never want to know, that in English "The Dasein" means something like "The Being There."
My own "The Rabbit of Usk,and/or Saint Timothy," like "The Dasein" or "The Being There," is also a something around which to arrange thinking with words. But unlike "The Dasein," or "The Being There," which are both the same thing in two different languages, The Rabbit of Usk is one thing and Saint Timothy is how The Rabbit of Usk defines itself. In other words, I'm not so much concerned with a definition in which to find an understanding of a something that might actually be true, as I am looking for a narrative in which to find solace. And I'm fairly sure that whatever you are trying to add to "Being," whether it is "Time" or "Nothingness" or "Technology" - and the list goes on - you are too.