Japan¡¯s introduction of joint custody from April 1 is sending sparks flying on both sides of divorced couples: high expectations from the parent who has been sidelined from child-rearing, and deep fear from those who have been victims of domestic abuse.

Until now, sole custody has been the only option available for divorced couples. But under the new system, parents will be able to choose between sole custody and joint parental authority after divorce, much like many Western countries. If the couple cannot agree, family courts will decide the custody arrangements for them.

With parental authority at stake, abuse victims¡¯ looming fear of the possibility that their ex-spouse could once again be in their lives is real. But the frustration of the current sole custody arrangement for a noncustodial parent is also hard to ignore.

Emi Ishikawa, 44, a domestic abuse survivor, said she fled with her then-1-year-old son five years ago after she could no longer bear her ex-husband¡¯s verbal and psychological abuse of her and their child.

¡°The verbal abuse began after we got married,¡± said Ishikawa, using a pseudonym because she fears being located by her former husband. ¡°After I gave birth, it escalated. He would call me stupid, mock my appearance and scold me for hours over miniscule things like forgetting to weigh my newborn.¡±

Ishikawa¡¯s then-husband would often lose his temper while he was driving, shouting at her to die while honking the horn over and over, she said. He abused their son as well, she alleges.

¡°He would tell the baby every day that there was something wrong with him, that he was sick,¡± she said.

Unable to take the abuse any more, Ishikawa packed as much as she could in a backpack, and fled with her infant son while he was at work.

Ishikawa was able to get a divorce after six months, not because of her husband¡¯s abuse, but due to his infidelity, as she was told by lawyers proving abuse would be too difficult under Japanese law. Her former husband has not had contact with their child since.

But the incoming introduction of joint custody has brought new anxiety of her husband possibly stepping back into her and her son¡¯s life. Parents who divorced before the law takes effect will be able to apply to change an existing sole custody arrangement after April 1.

Family court judges are not allowed to grant joint custody in domestic violence cases. Still, Ishikawa is not sure if she will be able to prove her case.

¡°To be honest, I am truly scared,¡± she said, arguing that the mental burden on victims will begin long before any court ruling.

¡°For victims, the...