Because Lily Adventuresses! Episode 2 has the premise of four playable characters who are able to greatly enhance their weapons by inserting tiny creatures that willingly turn themselves into cubes into the weapons' slots, I've been browsing relevant posts about them.

Since there's no way to implement positive status effects in RPG Maker 2000 (2003 onwards did so), the usual way of one character transforming into a more powerful form is to implement switches or parallel events where the base character is switched out for the transformed character, with higher stats and stuff.

But for this game, I'm doing things the old-fashioned way. In the Items tab of the Database menu, I just have to duplicate a weapon, and infuse additional stats into the duplicate. And when times call for transformations (e.g. boss battles), I just have to use the following event commands in sequence: Change Items (add transformed weapon), Change Equipment (equip transformed weapon), proceed with the rest of the battle, and win the battle itself. And by battle's end, Change Equipment (unequip transformed weapon), then Change Items (remove transformed weapon).

The full game will have a boss battle at the end of each chapter, and the characters will be mandated to upgrade their weapons at the beginning of each chapter, so the possibility of one character not upgrading their weapon will be moot.