To me that is the purest friendship. Between 2 souls.

I answered 'yes' but am honestly puzzled by the question. By reason do you mean looking for some advantage or something tangible? Or do you mean that it's hard to put your finger on the reason? I would say that most of my friendships are with people who I like and admire. I have nothing to gain from their friendship except the joy of being with them. But for each I could tell you which traits or characteristics of theirs I like.

If two people enjoy spending time with each other then that's all that matters. Eventually the shared experience of friendship will become the reason that you're friends.

It seems there is always a reasohn.

No. There's always SOME reason.

I think there is always a reason that we become friends with people, whether it's shared interests, likeable qualities, etc.. It's merely a matter of looking hard enough to see the reason or reasons.

Yes, as long as you don't have a reason not to like them.