Shulk and Rex dated girls who were part machine. That's actually kind of neat really.
Except Blades wasn't even part-machine in the first place? If we consider Blades as their own species and with the knowledge that they became Titans after several loops then it could be chalked as Blades having different physiology than humans. As what we know about the 1* rarity blades, which has more of 'robotic' look than the higher rarity blades, one can argue that these specimens represent the base standards of what Blades actually look beneath the skin and clothes. They could survive beheading or mortal injuries as long as their 'real' body, which was the core, is still intact, so Blades are closer to single-celled organism than actual living biological multi-organ creature.
