Requirements:
- action, adventure series
- some developed romance (preferably no harem or a small one)
- little to no ecchi content (if possible without prevy MC, accidental acts of perverdness and so on)
Extra points if female character\s has interesting personality and is not a loli.
Those are a little contradictory and it's hard to find all 3 in one series. For example, Tate no Yuusha no Nariagari (Novel) has the action, adventure aspect and is super low on ecchi content*, but romance is mostly undeveloped. When there developed romance, there is usually some ecchi content (I can read it if it's just a little), but I seriously dislike ecchi content in series that have no romance whatsoever. Last but not least the two WNs that had no harem (Risou no Himo Seikatsu (Novel), Seiun o Kakeru) also didn't had any action, adventure aspect.
Gun-Ota ga Mahou Sekai ni Tensei Shitara, Gendai Heiki de Guntai Harem wo Tsukucchaimashita!? (Novel) is close to what I'm looking for, but I wouldn't mind if it was a bit less ecchi (whats with the washlet fetish), the heroines had more personality. From what I heard another problem is that:
Spoiler (mouse over to view)
MC's harem steadily grows.
While I didn't mind all the gun trivia in the book, reading them in Japanese was a pain (lots of specialised vocabulary).
*Out of what I read of the series, there was at least one exception, but it's better to not talk about it...