Working blindfolded is a tradition in some Reiki classes, meant to sharpen attention to subtle sensations in the hands. The idea behind this question is that removing sight might, over months or years, reshape the part of the brain that maps touch. That is a real area of neuroscience, but the specific claim here has not been tested.
What the brain science actually shows is encouraging in a general sense. Somatosensory cortical maps are not fixed. Decades of research on experience-dependent plasticity have found that increased use of a body part, or sustained training on a tactile task, can expand its representation in the cortex. Receptive fields adapt to the statistics of incoming sensory information rather than staying hard-wired. Short-term remapping has even been observed within a single day in some setups.
So the underlying mechanism is not science fiction. Attention and repeated practice can shape how the touch-processing brain is organized. A person who spends years attending closely to faint cues in the fingertips, with or without a blindfold, is doing the kind of focused sensory practice that map plasticity research studies.
The honest gap is the Reiki-specific part. No published, controlled study has measured the somatosensory cortex of Reiki practitioners before and after blindfolded training. There is no evidence that Reiki, as distinct from ordinary tactile attention, drives any unique cortical change. Any expansion that might occur would most plausibly reflect general attention and practice, the same as for a musician or a Braille reader, not a Reiki energy.
It is also worth separating two things that often get blurred. Cortical map reorganization is about how touch is processed, which is a sensory question. It says nothing about whether Reiki transfers energy or produces healing, which is a separate claim that controlled trials have not supported.
Someone curious about this could think of it as a plausible but unproven hypothesis. The plasticity is real. The blindfold practice is real. A measured, Reiki-driven map change remains a guess that no one has confirmed. For now the body of evidence supports attention shaping the brain, while leaving the rest open.