hundred, leader of 100 men, east-west path between paddies
佰 centers on the number one hundred, and by extension a leader of a hundred men or a path between rice paddies that runs east-west, likely from its association with a standard unit or division.
佰 combines 亻 (person) with 百 (hundred), likely to express a person in charge of a hundred men. The path meaning may be a later extension or a separate usage.
A person 亻 beside the number one hundred 百: imagine a leader standing before a hundred soldiers, or a path marked every hundred paces.
For ヒャク, picture a leader of a hundred men shouting 'Hya!' as a battle cry: 'Hya!' cues ヒャク, and the hundred soldiers charge.