Saving 80,000 Gold in Another World for my Retirement 6 (light novel)

Book excerpt: Joining forces with the ambitious merchant Lephilia, Mitsuha is on a roll in the New World. But now their inventory's been stolen by a jealous rival! She's not letting them get away, though. It's payback time-with the cunning use of her world-jumping ability, of course. In this volume, our heroine is cooking up even more storms: an exclusive club for young noble girls, a manmade island, and a new kind of weapon that'll knock a boy's socks off?! Sure, saving up gold coins for her retirement is important, but right now, Viscountess Mitsuha von Yamano is amped up to undermine her enemy and strengthen her own county's and kingdom's economic power like a full-fledged ruler!