Hello hello! Thank you for this question! In fandom circles NL can stand for "normal love," usually used to reference male-canon-character x female-canon-character shipping in a fandom. Popular twst_NL pairings include the Shroud parents, Puffy x Eliza and one that hasn't reached EN yet 👀

I checked with the definition available on pixiv to make sure ( https://dic.pixiv.net/a/twst_NL ), and it is explained that Twst is in an unusual situation because the identity of the prefect is being kept so vague. Normally a ship with a fan character would fall under the twst夢 and/or twstプラス (or twstプラスB) tags, but as the prefect is canon to the game and could be interpreted as female, some fans of the male-canon-character x female-prefect dynamic use the twst_NL tag for their work ^^