There is no evidence for any “spirit” of the type you describe.
One needs to believe because you don't know for sure. Humans need to belief a lot almost on everything.
Religion exists due mainly to an advocate about whether life continues to exist after death. Since no human knows for sure, not a single one, thus everyone literally has a religion as a common belief shared by humans with a similar thought. Science won't help that much because science is basically observation and experiment based. Long before the emergence of science, humans already defined that whatever spiritual doesn't lie in our space/time, including gods, ghosts souls/spirits and etc.. It means we humans can't "go there" to gather scientific evidence. In the end, it boils down to one's faith to believe whether they exist or not.
Everyone has a faith on whether life continues simply because 1) you don't know for sure, and 2) it concerns your life. You don't think that you need to consider the possibility of what could possibly happen because you assume that nothing happens more likely developed from the absence of evidence. Humans have the basic instinct of concerning own life unless you assume it won't go beyond the point of death. This is where your faith is, perhaps without your own awareness (possibly as a result of your faith being firmly developed through education and out of the fallacy that the absence of evidence being the evidence of absence).