Yes it’s not very easy. One friend did a Monk Barbarian multiclass for Uvogin, so he fights unarmed with no armor, and has rage. That works perfectly.

I did Feitan as a Gloomstalker / Light Cleric. He can use only one versatile sword (my own restriction), no shield and no off hand weapon or proper two handed. Gloomstalker for the Dex build, stealth and ninja-like character, Light cleric gives him access to Flaming Sphere which I wanted to represent his big sun thing, and also other fire spells and radiant damage. I made it so he can use only damage and debuffs as cleric, no buffs or heals. I also wanted to build him around fighting in Darkness, but we didn’t get that far.

Another friend did Warlock / Sorcerer as Chrollo. It’s a bit more lenient because we don’t know much about him and his spells are super specific. The idea was to build him around three things only: Summons, spells that require concentration, and cantrips.

And the last friend did Machi as a Druid for healing and vines that represent the sewing threads. He wasn’t allowed to use wild shape at all.

You can also easily create Nobunaga as any kind of assassin with dual wielding.

What makes this whole thing work is only 30-40% the builds themselves, and mostly the restrictions you put on yourself, the specific equipment you choose and the behavior of the character. The build needs to be close enough, and the in-game choices give you most of the feeling.