One permanent is sacrificed each time an opponent’s source deals damage to Michiko Konda’s controller. The amount of damage doesn’t matter.

Sources that deal damage multiple times (such as creatures with double strike) will trigger Michiko Konda multiple times.

Spells that deal damage repeatedly trigger Michiko Konda’s ability each time they deal damage. For example, a Glacial Ray spliced onto another Glacial Ray triggers the ability twice (once for each “2 damage” event from the Glacial Ray).