the reject/go no go decision is up to the captain at every airline I can think of unless the captain is incapacitated. the copilot does not make the decision and the captain is the one to actually take control of the plane and reject (assuming the copilot was flying the takeoff).
I know of at least one airline where a co-pilot can call stop in certain circumstances and if they are handling they also carry out the initial actions because they also handle their own power.