The wife of a victim of the Kyoto Animation studio arson attack four year ago says she wants a harsh sentencing for the defendant, adding "he used the most cowardly means to take our family's lives."

Aoba Shinji has been charged with murder and arson for killing 36 employees of Kyoto Animation and injuring 32 others when he doused gasoline and set fire to the studio in July 2019.

Arguments continued on Wednesday on the circumstances that led to the crime, which would affect sentencing.

Six bereaved family members spoke in court, while three others had their statements read out.

A woman who lost her 34-year-old husband, who worked as an animator, said their daughter was 16 months old at the time and had not yet begun to speak.

She described how her husband had been excitedly wondering how his daughter would first call him.

She said an irreplaceable family member was lost in an instant in the most cowardly way, and added that she wants the defendant to accept the ruling with an understanding that each victim was loved and had loved ones too.

A man who lost his 44-year-old wife said she was killed for trying to make others happy.

He said it is hard to see their son bearing the loss and trying to move on.

He urged the defendant to face up to his crime and feel remorse for the victims.

Aoba listened with a fixed gaze at the families, and occasionally closed his eyes.

More families are scheduled to speak on Thursday.