Considerations

The human body was not absolutely opaque. This was something that an overwhelming majority of people were not aware of. In reality, the human body was translucent; It allowed light to partially pass through it. This was partly because of the fact that seventy percent of the body of the human body was comprised of water, which was perfectly transparent. This was what largely gave the human body its translucence.

The translucence of the human body could even be tested and measured at any give point in time.

One need only place a bright and intense source of light behind one's thumb, and one would notice the thumb glowing red due to all the light passing through and bouncing off the red blood and flesh, becoming red.

("If that is what is happening with the circulatory system of Martial Seniors, then that would explain the red flowing lines across the body,') Rui realized in excitement.