if you go on the fact that dreamstone can absorb magical energy, along with the MM is absorbing magical energy from lavos and lots of it, then apply it to simple scientific laws like difusion, it would be natural that the masamune conecting with the MM (when you hit it) would start to share the energy from the MM which would lead to more being on the masamune (the masamune in effect absorbing the energy from the MM). the question is why/how does this energy replenish frogs hp? if anything you would expect to replenish his mp or make the sword more powerful, the latter being unlikely you would expect the first, hmm.