This manga is great, but urgh, that shit on page 16-17..... It's not just that the mass needs to touch to reach infinite gravitation force, it needs to occupy literally the same space on a particle level. The equation of gravitational force is all about the *center of mass*, not the *boundaries of the mass*. So yeah, if the center of mass of two elementary particles are exactly the same, of course it has infinite gravitational force because it's actually *the same particle*. As far as we know, it's not possible to break down an elementary particle [like a photon or electron], so this actually makes sense--it is infinitely bound to itself (although if e.g. an electron annihilates with an antiparticle like a positron, it'll change form and each part will usually become a photon).
