I'd say Lala.
Although, I'd say both of them deserve to be at this side. Yes, Haruna was there from the beggining and seeing how Lala got close to Rito, she was shy and afraid to confess her feelings for him due to the incredible bond of friendship she was developping with Lala who has became her best friend now, so it must have been hard on her, even though she's known Rito for a far longer time. But, let's not forget, "the early bird gets the worm", and Lala took that ocassion to be close to Rito as she lived in her house and met the Yuuki family which she even got their blessings from the parents. Also, Haruna had multiple ocassions too, including the ones before Lala entered in the scene, in middle high school with Rito. It would feel ackward if Lala were to be gone just like that knowing she's considered as a part of the family, even without the engagement or boyfriend-girlfriend matter. Yes, at the beggining, it was to escape the whole engagement deal (besides, after seeing all of these candidates, we all know why she ran from home, no woman would like to be married to on of these guys), but afterwards, she developped feelings towards him and even though Lala loved him, she understood her own selfishness as she didn't respect his own feelings and as she recalled the way she abruptly entered his life, so that's why she restarted everything to zero to make a new fresh start, even by knowing Rito also had feelings for someone else. Although within almost two years she's been living with him and got the "I possibly like you" confession from Trouble-Quest, that confession was a turning point for Rito as his own self became more aware of Lala, so I wouldn't consider that "small confession" to be insignificant since it was the biggest confession from Rito we've seen in the series so far. Make no mistake: the fact that you're living with someone for almost two years doesn't mean you'll win their heart or you're hugging them for yourself, otherwise Rito and Lala would had been officially known as a couple from a long time ago and/or Lala would had been pissed hearing
Spoiler (highlight to view)
Haruna's confession in chapter 118.
, seriously.My point is? I believe both Lala and Haruna are exactly the best friends ever:
Spoiler (highlight to view)
Haruna confessed her feelings for Rito to her and Lala actually felt bad because she wasn't able to notice that before she told her and even encouraged her to confessed to him, but Haruna replied that she's not ready for this yet
. Last time I checked, that's a true example of friendship shared by best friends. We all know that Lala isn't the backstabbing type, so I conclude that she won't try anything to hurt her best friend, even though she doesn't want to lose Rito. Breaking heart is far from being in Lala's personnality, I wouldn't even be surprised if she actually sacrificed her feelings for Rito for Haruna's happiness. I believe it is useless to try throwing missiles into this "who's to blame and who's not, who deserved Rito or not" matter, since both of these lead female characters in Rito's life deserved rightfully to be at his side. I believe they both have proven themselves to be worthy of him: Haruna was in Rito's heart from the starting, but Lala, due to her efforts, made him realized his feelings for her and came to care a lot about her. I myself am rooting for a Lala-Rito ending, but I wouldn't be upset if Rito would go towards Haruna, as long as Rito takes a long time to think about it because at the end he will be the only one who will have to make the final choice.Spoiler (highlight to view)
To conclude this, Rito only needs to be aware of Haruna's feelings, that's the only thing left. Lala and Haruna have done their part, now it's up to him to step up. I'm also positively sure at 100% that the other female characters might step up too, but they won't stand a chance against Lala & Haruna, not even Yui.
I'd think Lala would be the one, because if she goes back to Deviluke empty-handed, she'll be forced to marry some space bastard she doesn't like and I don't think Rito will be able to live peacefully knowing this. As for Haruna, she is used to seeing Rito and Lala togehter, so it wouldn't be an amazing shock for her.
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She's not weird. She's just...different.... Who said aliens were weird?? Besides, there might still be a plot twist...
It seems it about the only thing he is good at to boot.