Training multiple character LoRA (Illustrious / Pony)

Here are tips for creating multiple characters in the same LoRA. This works best on illustrious but can also work with pony.

Benefits

Saves space
Can train images with multiple characters without cropping them (useful if characters appear together frequently)
Can generate images with multiple characters more easily
Works as a style LoRA if characters are from the same source (same artist or from screencaps)
If multiple characters wear the same outfit then the LoRA also becomes a costume LoRA

Tagging recommendations

Tag each character's name and remove appearance tags that are always the same (for example, hair color, hair length, eye color, etc)
If two characters appear in the same picture tag both and use the correct gender tags (for example, 2girls, if there are two in the picture or 1girl, 1boy, if there is a boy and a girl in the picture)
Put character name tags at the front of the file
Don't use the same clothing tag for multiple characters unless they are wearing the same outfit. For example, if two characters are wearing shirts you could tag one as t-shirt and one as collared shirt. Or if they are different colors, specify the color like blue shirt and red shirt.

Example image tags

Character 1

takeuchi yuka, 1girl, solo, hair ribbon, fingerless gloves, serious, frilled shirt, orange skirt, underbust

Character 2

kubota jun, 1girl, solo, headband, building, knee pads, yellow puffy sleeves, elbow pads, hair ribbon

Character 1 and 2 in same image

kubota jun, takeuchi yuka, 2girls, fingerless gloves, battle, duel, yellow puffy sleeves, orange skirt, frilled shirt, underbust, hair ribbon, headband

Balancing image count

All characters in the LoRA should be trained with a similar number of images. If you don't have the same number of images you can use duplicates. For example, if character 1 has 20 images and character 2 has 40 images.

Kohya training

Use the repeat folder feature with the folder names:

02_character1

01_character2

Each of character 1's images will be trained twice so that character 1 has the same amount of training as character 2.

Civitai training

Because civitai does not support repeat folders you can select the files you want to duplicate on your computer, CTRL-C and then press CTRL-V for as many duplicates are you need.

Choose train character and upload the zip file in the civitai trainer

Check shuffle tags, clip skip 2, and choose to keep 1 token. All other settings other than epoch can be left as default.

Raise the epoch count until the buzz cost rises above 500. If you find character likeness is not strong enough try raising the epoch count by 5 or 10 next time.