I thought about what implications could always be valid: eye color isn't valid because the character could be with the eyes closed (besides the fact that eye colors aren't always respected). Iconic clothing items or maneirisms, however AWESOME (hakurei_reimu -> armpits) aren't valid either, because the drawing could have the character without them.
Some physical characteristics could be implied, however. I think hair color is default enough, and boring enough to add separately, as to make the following implications valid: (I marked the ones I feel can be troublesome with a ?)
hakurei_reimu -> brown_hair
kirisame_marisa -> blonde_hair
rumia -> blonde_hair
rumia -> short_hair
daiyousei -> green_hair
daiyousei -> fairy_wings ?
cirno -> blue_hair
cirno -> short_hair
cirno -> wings ?
hong_meiling -> red_hair
hong_meiling -> long_hair
patchouli_knowledge -> purple_hair
patchouli_knowledge -> long_hair
izayoi_sakuya -> white_hair
izayoi_sakuya -> short_hair
remilia_scarlet -> blue_hair
remilia_scarlet -> short_hair
remilia_scarlet -> bat_wings ?
flandre_scarlet -> blonde_hair
letty_whiterock -> short_hair
(letty's hair can be all kinds of whitish color in fanart)
chen -> cat_ears
chen -> brown_hair
chen -> short_hair
alice_margatroid -> blonde_hair
alice_margatroid -> short_hair
lily_white -> blonde_hair
lily_white -> long_hair ? (don't know enough art of her to see if this is followed)
lily_white -> angel_wings
lunasa_prismriver -> blonde_hair
lunasa_prismriver -> short_hair
merlin_prismriver -> blue_hair ?
lyrica_prismriver -> brown_hair
lyrica_prismriver -> short_hair
konpaku_youmu -> white_hair
konpaku_youmu -> short_hair
saigyouji_yuyuko -> pink_hair
saigyouji_yuyuko -> short_hair
yakumo_ran -> blonde_hair
yakumo_ran -> short_hair
yakumo_ran -> fox_ears
yakumo_yukari -> blonde_hair (long_hair not added because it's not always apparent)
If this idea is appreciated, I can put up implications for the other windows games.
Updated by cleartailcat