Well maybe that’s what the author was going for, but there are tons of holes in there:
-why did Takt transfer with Shizuku ? Maybe I missed why, but if he doesn’t know about her disease, then it doesn’t make sense. Author says Takt is possessive about Riku and doesn’t loves Shizuku. Then why would he left him to follow her ?
-Shizuku does all of that to preserve her group, but starts having secrets with both of them. Her very behavior makes Riku thinks she’s not dating Takt for good reasons, and that she may like him. What if she had succeeded in seducing Riku ? After she dies, their friendship is dead, Riku is too kind to keep that secret. It’d have made more sense that Takt was forcing her to date him imo.
Shizuku sounds very selfish and extremely dumb. She does all of that thinking that Takt loves her, and seeing how she behaves with Riku, she probably also knows that he likes her. Know that I think about it, I don’t remember her seeing getting jealous when he gets freaky with the other girls.
About the kissing, if i remember correctly it was in the early chapters, they were going back from school, Riku part ways with them and Takt kisses her on the spot. Good ntr vibes
Takt didn't transfer with Shizuku. Shizuku was never transferring schools but rather she left school for an extended period of time to prep for her surgery. Shizuku, her mom and the teacher came up with the transferring schools story as Shizuku did not want to tell any of her classmates what was really going on as she wanted them to focus on their tests to get into college. Instead, the day that Riku found out from the teacher that Shizuku was gone and not coming back, he rushed to find Takt but Takt had already left school to go visit Shizuku as Takt had just found out about Shizuku's illness.
It's not shown who told Takt about Shizuku for him to show up to where she was staying after the surgery - I'm assuming Shizuku called him as the next chapter's discussion between Shizuku's mom and Takt left the impression that this was the first time Takt was speaking to the mom. So I have to assume Shizuku probably told Takt where to go as now that the surgery is done the deal is also done and she wanted to come clean about everything.
Takt confessing to Shizuku really put her on the spot and probably did not give her any time to really sit down and think about it. I'm assuming she answered him right then and there and came up with the deal. The confession is shown (without words) in chapter 67 and it seems like she answered him very spur of the moment.
Yes, her keeping secrets from both of them does have the potential to blow up the group once she's dead. Yes, her behavior with Riku has the potential to destroy Takt & Riku's friendship once she's dead. I think she made a split decision to date Takt and immediately regretted it but felt there was nothing she could do. She decided to pursue Riku because she realized she was most likely going to die and her love for Riku overpowered everything else. She didn't want to regret not being with him.
I believe Shizuku thought she was being unselfish by hiding the truth from Takt & Riku as she didn't want them to waste time feeling sad for her. I don't agree with her action there but I can understand why she might think the way she did. I think she suspected Riku liked her but he didn't really confirm it until Chapter 42 at the beach house when they're in bed together. Riku mentions he doesn't want anyone touching her but him and that he didn't want her to go out with Takt or anyone else. He'd been wondering why she wasn't his. Shizuku responds that she's happy Riku has been thinking about her that way but that she can't be his. In the moment, we're supposed to think that the "I can't be yours" means she's Takt's but I think it means overall that she can't be Riku's as she'll be dead soon. This leads into Chapter 43 where Shizuku's licking Riku's cum off her fingers and Riku is protesting - she says she wants Riku to remember she was the first to do that with him. She goes on to say "Even if you were to start dating someone, or get married in the future, you'll always remember that I was your first."
This is the overall goal of Shizuku. She wants Riku to be her first and for her to be his. That way he'll have lasting good memories of her after she dies. She goes on to further state that it's not that "I want to have my first time with Riku, but rather I want Riku to be the one to initiate it." She wants Riku to take a stand for once and fight for her. It's not completely fair to him as, as far as he knows, the relationship between Shizuku and Takt is real and he doesn't want to betray his friend.
All in all, it's not the best writing from the author but I can kind of see where they're going with it.
Regarding displays of affection between Shizuku and Takt - she ruffles his hair in Chapter 1, she touches his back to greet him in Chapter 2, she's linked arm in arm with him in Chapter 7, again linked arms in Chapter 16 as well as holding hands, Shizuku has a bandaid on her neck in Chapter 17 which might be covering a hickey that Takt gave her after Chapter 16 but it's not confirmed, I got to Chapter 27 and still hadn't found anything else between them so I'm going to stop for now.
However, after skimming through Chapters 1 through 27, I realized that I might be mistaken as to when the deal between Shizuku and Takt took place. I just assumed it was right after Shizuku accepted Takt's confession but now I'm thinking it came later.
I think Shizuku accepted Takt's confession and then proceeded with zero displays of affection - no kissing, no making out, no sex. I have a feeling that while she accepted to keep the friend group together she wasn't willing to do anything other than maybe hand holding or linked arms.
In Chapter 16, Takt sees Shizuku casually touching Riku's back and stops walking with the group. Riku notices and Takt says he has to go and gives Shizuku a serious look. She reacts and leaves with him. You see them walking away with linked arms then they stop and you see a speech bubble of Takt talking to her while pointing to someplace. She nods and then Takt takes her hand and drags her off while side eyeing Riku. Here's what I think happened there.
Takt, noticing more and more that Shizuku and Riku are getting closer despite Takt's attempts to block them by dating Shizuku, takes Shizuku somewhere to set some rules. I think he probably asked her what the heck is going on and why is she all lovey dovey with Riku and won't even kiss him even though they're dating. I think it's at this point that Shizuku comes up with the "deal". She'll agree to kissing and making out but no sex until April of their 3rd year. She makes the deal to keep Takt happy and the friendship group together. Takt accepts as it he thinks it'll mean that Shizuku stops being lovey dovey with Riku and he gets a little extra out of it. Maybe he did give her a hickey and that's why she had a bandaid in Chapter 17 or maybe it's a red herring and the place they went had a bunch of mosquitos - who knows. Maybe we'll get a flashback of the deal or maybe the author will just gloss over it.