First off, I really loved this series, it was so good. And the first part when he's taking care of her is cute and heart warming, like a father-daughter relationship and I was happy with the ending. That being said, the fist part is from the point of view of Daikichi, so of course he would only look at her as a daughter.
Think about it, the author had set up things that would point to this ending if they decided to go with it.
One of them being Rin saying that Daikichi is not her father, also Daikichi never really being able to end up with Kouki's mother, and also Rin not really being able to go for Kouki at all.
When you think about it, the author obviously had this type of ending in mind, even if she didn't go with it.
Also, I believe that any type of love can be if you truly go for it. And I don't like it when those people bash it because they just don't think that it was a suitable ending. I get that you are entitled to your opinion on whether you liked or not, but does any one have to go on a hate rant about people who like it, because they hate a relationship? You don't like then ending then fine, but don't bash others who did, it just makes those ranting looking hateful and pathetic.
But anyway, if you're looking for a nice family type story, this is a definite read. And if you hate that
that the two main characters plan to marry at the end and have a family together even thought the man raised her as a daughter and the woman never really saw him as a father but rather a man who takes care of her in place of a parent
then I suggest that you do like others say and stop after volume 4.