After she heard Kodaka said the "you only need 1 best friend whom treasure you as much as 100 friends" thing and knew that Kodaka also thought of him (Yozora as Sora) as his childhood best friend, Yozora was happy. She talked to herself (well, Tomo-chan) about her past and wonder what will happen if she could say the unspoken words back then. Sena overheard it, so here Sena knew Kodaka and Yozora past sooner.
Yozora then suggested the club to do lover simulation as their next activity due to a say "from friend to lover" and insisted Kodaka to agree, so they're going to simulate a date between a lover. And since Kodaka is the only male while there's 2 females (Yozora didn't count Kobato and Maria since they're still little girls
) Yozora already prepare
Amidakuji sheet for herself and Sena to pick who will become Kodaka's lover on this date.
Sena was spacing out this whole time thinking about Yozora and Kodaka status quo so she didn't really hear about the plan. But when Yozora told her to do her part of Amidakuji, Sena pretend to know and excitedly grabbed the result sheet from Yozora. And it was Sena who won the game thus she will be Kodaka's lover (she was surprised since she didn't hear that this was only a simulation ^^).
Unbeknown by Kodaka and Sena, actually Yozora cheated the result sheet so whatever lines chosen, one will be a winner. So it depends on who saw the sheet faster, and as Sena grabbed it before from Yozora and saw it first, Yozora couldn't do anything beside accepting Sena will be Kodaka's lover on the simulation date. Yozora wasn't give up yet though. As this was a club activity, Yozora will be there on the date too as an observer.
Yozora tried to ruin Kodaka and Sena simulation date by gave the couple specific things-to-do-on-the-date schedule memo they had to follow, like watch certain movie and went to a restaurant. But with the couple luck it backfired Yozora; the movie Yozora thought shitty movie was actually a good love drama one, and even when the restaurant Yozora wrote on the memo supposed to have bad service, when the couple came they got the best treatment because they won the lucky couple thing.
Tired of Yozora's interference, Sena grabbed Kodaka's hand and ran from Yozora when they had the chance. Sena wanted to go to game center to win Renka (Tomo Plus game character) doll from UFO Catcher machine and she wanted Kodaka to do it for her since this was their date. After many failed attempts Kodaka finally got it, so excited for a while they forgot they're too close. The couple then continue their date, they went to other places.
At the end of the day, Kodaka and Sena went to the park. Sena as usual compared their date with her experience with Renka on galge and said that this date with Kodaka is pretty exciting too. Kodaka said that he wanted to do this again, it made Sena blushed with the thought of dating Kodaka again and went tsundere said that it's not a bad thing for her. The thing is, what Kodaka meant was the club activity. Sena disappointed that Kodaka still thinking Neighbor Club even though they were on a date.
It made Sena thought things like 'was it because of Yozora the club is so important for Kodaka?', 'but Kodaka doesn't seem to realize Yozora is his childhood friend yet?', 'childhood friend is basically a friend, right?', 'so Kodaka doesn't need to be on club anymore, then I can't do things with Kodaka anymore?'. Yozora then finally found the couple and she approached them. By then, Kodaka thought what Yozora was doing. That made Sena snapped. "So, it IS Yozora. You wanted to go with Yozora instead me, right? Both of you are already friend from the start. I knew it that you and Yozora are childhood friend!"