But in rare cases, lightning beats ice (it's just water) and is beaten by fire because heat increases resistance to electricity (at least in metals; in air, heat decreases resistance, so fire will make lightning stronger...?).

What element can beat lightning?

Fire is weak against water and strong against wind, which is strong against lightning. Earth is strong against water but weak to lightning. When two elemental jutsu are used against each other, the weaker element does 25% less damage.

What does lightning and fire make?

Plasma, Purton (Fire + Lightning): the Element of the Sun, as it is refered to. It is a potent mix of Fire and Lightning chakra that allows one to create a substance that has the brightness and burning power of the Sun.