In the sumo ring at the precinct of the Kamegaike Hachimangu shrine in Sagamihara west of Tokyo, two hulking wrestlers held up toddlers wearing tiny sumo belts and aprons to try to make them bawl.
Wrestlers sometimes shake the babies gently to encourage tears.
"My boy was crying from the very beginning and I felt a little bad," Tomoyo Watanabe, the mother of Zentaro, told AFP.
"But as I watched my baby crying, I was praying for him to grow up healthy and strong after this event."
The "crying sumo" festival is held at shrines and temples nationwide, to the delight of parents and onlookers.
The ceremony is believed to date back more than 400 years.
The rules vary from region to region - in some places parents want their offspring to be the first to cry, in others the first to weep is the loser.
In the Sagamihara event, which has been running since 2011, the babies accompanied by parents and grandparents were first taken before a Shinto altar and purified by the priest.
Pairs of toddlers were then brought into the sumo ring - where most of them were bawling even before facing off against their rival.