While Japan revised in 2017 its criminal law to impose stricter penalties for sex offenders for the first time in 110 years, critics of the legislation have looked to Sweden's consent-based sexual offense law as a guide for further amendments.

The Scandinavian country's legislation, promulgated in 2018, states sexual acts require voluntary participation. Under the slogan of "yes means yes," sex without explicit consent would be deemed rape.

Several European countries, including Germany and Britain, already define rape as sex without consent.

The law also stipulates that physical violence, threats and coercion are no longer prerequisites for defining rape, according to Viveka Lang, a senior advisor at Sweden's Justice Ministry.

"A sexual offense is one of the most intrusive acts that you can be exposed to," she said in a recent interview with Kyodo News during a visit to Tokyo.

"It's more intrusive than other acts of violence. You can't assume that it's alright to have sex with anyone, just as you can't just take something without asking."

Japan's revised Penal Code broadened the definition of rape to include male victims. However, it did not drop a requirement that the perpetrator must have used force or threatened the victim to establish an assault as rape, which some say does not go far enough to protect victims.

The Swedish legislation, in contrast, stipulates that the sexual act is illegal if it's not voluntary. The law is applicable, for example, if the victim is simply passive and also covers sexual acts that do not involve penetration.

However, there is no legal definition as to what it means to "participate voluntarily," and it is up to the participants to consider whether their "voluntariness" was expressed in words or actions, senior legal manager at the Swedish Prosecution Authority Hedvic Trost said during a press conference in Tokyo.

The Swedish legislation on sexual assault and rape had been amended in 2005 and 2013. Although both revisions extended the net for what constituted a crime, they were not consent-based as the government at the time believed that there were too many drawbacks, according to Lang.

"But the debate in Sweden didn't stop. People were not happy about the legislation that we had," she said.

There was no specific case that gave rise to the latest revision to the law. "It was more like a long process, where little by little, people came to the conclusion that we must have a consent-based legislation," she said.

According to Lang, many were initially apprehensive about amending the legislation due to fears that a consent-based law would place further pressure on the victim to answer intrusive questions when they are already exposed to an arduous legal process.

But Swedish legislators who visited Canada and Scotland to ask about consent-based laws which they had already in place, determined that it was not as big of an issue as they had originally assumed.

"The legislation puts more focus on the perpetrator -- what did he or she do to inform that this is consensual?" Lang said.

Several countries have since looked to Sweden's revised law as an example to amend their legislation, including Iceland, Finland, Denmark and Norway. Spain, which has been in contact with Sweden, will become the 10th country in Europe to define rape as sex without consent, its government has announced.

However, the law has also garnered questions regarding the possibility of false accusations, with some asking whether people would be more inclined to lie about a sexual encounter because the Swedish system seems to provide victims with broader support.

Regardless, the false accusation rate is "extremely low," Lang said, although the exact rate is not known.

"These crimes are very difficult to prove," said Trost. "False accusation is quite a severe crime and we can never be 100 percent sure they aren't there. It's happened before, but it's very rare."

The law, moreover, stipulates that a person must give evidence when reporting a rape or sexual assault -- a statement alone is insufficient. However, talking to a friend about the incident to have someone who can corroborate the story can be used as evidence for a conviction, she said.

Japan's recently amended law still requires violence or coercion for a sexual violation to be officially defined as rape. At the same time, the legal age of consent is set at 13 -- one of the lowest among the developed countries.

Activist groups in Japan, such as Flower Demo and others, are calling for the introduction of consent-based provisions and raising the legal age of consent when a debate on further revisions to the penal code is expected to take place later this year.

"I think Japan has to find a way which is suitable here. It's important to get acceptance for the law, or else people won't follow it," Lang said. "The more you speak about it, the more it becomes obvious for people, even those who were against it. To raise awareness is important."

Sweden will release a report in June on how the legislation has been applied since its implementation.