The original question was worded as follows:
I was just wondering if there is any word we can use as opposite of
I started using my own words randomly like "kill-hard hater"
"kill-brutal hater" and I may discover few more in this pattern if I
don't find the answer :P
I remember being very confused when I first read this question; the notion of "kill-hard hater" sounded like nonsense to me. But then someone offered the answer fairweather fan, to which you replied:
-1. per the wiki link "fair-weather fan:Fans who only follow their team when they are winning." this is wrong answer
Okay, I'm going to pause there, and offer you two hints:
1) Don't end a question with ":P". That's an emoticon signifying sticking your tongue out at someone; it is not a respectful gesture. Wikipedia lists one possible interpretation as "blowing a raspberry". I don't think that's a very good way to end your question, particularly when it might be a little confusing to begin with. (I doubt you meant to show any disrespect, but it probably didn't help your cause.)
2) Don't downvote someone who answers your question, and call them "wrong". If someone has misinterpreted your question, put your energy into clarifying your original question instead.
(I'm only stating a theory here, but those two things combined may have made it difficult for some in the community to regard your question as a serious one.)
[end of pause]
Later in the dialogue, Kevin wrote: I think Inglish is looking for a term for someone who really hates a team as in "I'm a die-hard fan of the Red Sox which, of course means I'm a [XXX] of the Yankees"1
Maybe that is what you were looking for? If so, that would explain why you dismissed fairweather fan, which, as others later pointed out, is a perfectly suitable antonym for die-hard fan:
Fairweather fan: Fans who only follow their team when they are winning.
Die-hard fan: Someone who possesses extreme, absolute or complete loyalty even if facing defeat or hopelessness.
I think that Kevin's intepretation of your original question would be well-received by the community, if it was posed in that way: supported by an example (rather then steeped in silliness), so that it was more clear and less confusing.
1If this example makes no sense to you, try substituting "Manchester United" and "Liverpool".