Thanks to a series of translated interviews with Yakuza series directors and producers, specifically one with Masayoshi Yokoyama, we learned that in Yokoyama’s personal opinion the series protagonist Kazuma Kiryu is probably a virgin. Yokoyama has long been involved in the Yakuza series, being in charge of script, sound direction and stage direction for all the numbered games as well as Kenzan and Ishin, and has been a producer since Yakuza 5.
The translated interview, which can be read in full here, touches on Yokoyama’s approach to the characters and the inspirations he takes in portraying them. When it comes to Kazuma, Yokoyama mentions that Kazuma is probably a virgin. While this is just his own opinion and is not official in any way, the notion went a long way in the development of the character. Yokoyama also cited that this what if scenario is a fun discussion one could have at a bar between friends who are fans of the Yakuza series. [WARNING: Yakuza 1 spoilers!]