I was curious so I duckduckwent whether wario amd waluigi were also isekaid and I found out that waluigi is super cool

https://www.reddit.com/r/Marioverse/comments/sadwr8/are_waluigi_and_wario_from_the_mushroom_kingdom/

But who was Waluigi before he was Waluigi? Well, we have nothing concrete but perhaps there are a few clues….

Waluigi may be a botanist.

As originally proposed by u/TheBeanary, Waluigi has the “Vine Whip” and "Wall-Luigi" in Mario Strikers Charged. These are Waluigi's special abilities in the game, both involve plants.

Waluigi Island in Mario Party 3 is decorated with Piranha Plants that are subservient Waluigi, plus his Mario Party 3 duel mode partners is also a Piranha Plant.

Waluigi may have been a Construction Worker

As originally proposed by u/tokiro7 (and a few others, I’ve seen versions of this theory around since ~2014),

In Dance Dance Revolution: Mario Mix, Waluigi’s boss theme was Destruction Dance, a remix of the bonus stage music from Wrecking Crew, a game set on a construction site. In Mario Kart DS, Waluigi’s signature kart was the Gold Mantis, an excavator which would be used by construction worker. In Mario Party-e, the Waluigi’s Reign minigame sees Waluigi dropping hammers on Mario in what appears to be a construction site.

Finally, Waluigi is commonly associated with eggplants, most notably in Mario Superstar Baseball wherein his Power Shot, the Liar Ball, is unlocked by purchasing the Whiskered Eggplant and sees Waluigi’s pitch split into a baseball and an eggplant to confuse the batter. This may imply a connection to the Eggplant Men, who were employees on the Construction Site of Wrecking Crew.

Marios toad harem doesn't count?