I think the author directly revealed that 3 is the last doll made by the founder of the Global order.
And some rather clever people spotted that its pretty likely he is the same as Tobi's grandpa.
That would explain why he sticks with her.
He recognized her.
"If it lives it can be killed.
If it is dead it can be eaten."
Ronkong Coma "the way of the bookhunter" III Catacombium
(Walter Moers "Die Stadt der träumenden Bücher")