No, your right. It was designed to be as ambiguous as possible from the start, so its no wonder you may not have picked up on the subtleties of the relationship that IchiRuki shippers do.
But Kubo denies it being platonic, while at the same time denying it being romantic either, or atleast that was his view point in 2008.
But since then, he's come out openly teasing fans on their future possibility in certain interviews as opposed to shutting them down, so it seems to me, he has never thought of their relationship as one particular thing instead of constantly being in motion at different points, which i really like.
At some points she acts like a mentor, some points like a mother figure, other times like a best friend, and, at other times...