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 Spoiler

He was actually childhood friends with all three girls (Chitoge, Maria, Onodera), and all three also have keys. He also has a few other girls that like him, but are obviously not the promised girl. Ondera had a book from their child hood that Chitoge remebers, Chitoge has a diary, and various things could point to any of the girls really. And ofc they broke the opening mechanism of the pendant so they could prolong it as long as possible.

It hasn't been revealed who he gets with in the end (as it hasn't ended), while Chitoge does seem to be likely as she is one of the main characters, i'm personally rooting for Onodera (since she liked him first and he actually likes her back).

Looks like I really don't remember much, even got keys and pendants the wrong way round. Well what can I say? It's been what, a year?

 Spoiler

Wait, was Maria even childhood friends with the other two girls, because that was what I was talking about there, about the guy and first two girls hanging out as a trio when they were kids.

I'm honestly thinking Raku's memory might be fragmented, or some really crazy pomegranate is going on here.