Fusion technologies have been pretty widespread in the first world for awhile now. At the start using such technologies were seen as... unnatural, and in certain circumstances akin to a double suicide at minimum. However with more statistics and anecdotes the family and friends of the fusions noted that while the fusion was different than their friend and loved ones, they still noted that the people are still kind of there in a manner of speaking.
Whether or not their exact personalities were in the fusion the technologies had some limitations. The fusion process involved a lot of energy, and a decent amount of mass is lost in the process. Depending on how fast and efficient the process is the fusion will generally have anywhere from 40-60% of the combined mass. So even if in theory de-fusion was possible there wouldn't be enough stuff for even a full person.
Nowadays the fusion technologies give people a lot more options in how the fusion comes out. How much of which personality shows through, what gender the fusion is in the case of bisex fusing, ethnicity, etc. Even some people try to abuse the mass function if everyone involved wants to be shorter.
Now we see how the fusion technology will affect the life of...