the villains

SEYMOUR
Did you know that Seymour is a French name? I couldn't believe they gave a guy like Seymour a French name....oh, well. Anyway. Rikku practically hates Seymour's guts. Sure, he is a good leader, but the marriage proposal clearly upset Yuna - and Rikku cannot stand anyone who upsets Yuna. Besides, she is seeing the start of a beautiful relationship between Tidus and Yuna. How could her cousin marry in the middle of her pilgrimage?
When the proposal turns into a fight at Macalania Temple, the truth about Seymour is revealed. No way Rikku could allow Yuna to marry someone who killed their own father! So they kill him in the fight. And because an Al Bhed was in the party, the whole race of Guado gets revenge by attacking Home - further igniting Rikku's dislike towards Seymour.
And when the guy just won't DIE - and he kidnaps Yuna - that is the last drop. She cannot understand how someone can be so twisted as to kill their own family and then try to save the world by killing it.
I think there is no room for romance in this relationship.

SHUYIN
The Tidus lookalike. In the beginning Rikku was very hyped up about this, since they thought he was Tidus (which means that Yuna and Tidus could reunite!). But no. Shuyin is not a bad person, his anger towards Bevelle just got new heights when he and his lover Lenne were killed. It's really rather romantic, thinks Rikku. Love across time and death.
But when Shuyin possessed Baralai (after finding out he was possessing Nooj all this time) and started threatening people and iniatalized Vegnagun - that's when the YRP decided that he might not be completely right in the head. His anger had twisted him so he could not see straight. So they decided to fix it.
There is nothing romantic about RikkuxShuyin pairings, mostly because he is dead and so utterly devoted to Lenne. Rikku views this as romantic, no matter how much he might destroy the world while searching for his beloved.