An excuse I always used to hear for lingerie armor in otherwise serious settings is "It's to distract the enemy"
Maybe she trained to fight in a "flashy" manner over at her adventure school. It wouldn't be out of place in the story that pairs adventurers based on likelihood of boinking
Ignoring the various holes in that sort of plan, wouldn’t it be easier to just… invest in society to try and improve their training instead of just telling them to fuck?
Also even if they do seggs, if the goal was really to ''make babies'', the mother will have to immediately take a maternity leave. Theres no point in hoping for descendants if the woman already ded while adventuring