I wonder if succeeding at giving him head counts as "progress" in her cheating quest. They did finally cross some sort of line after all. Now that Riku's junk got some mouth action from her, that 120% counts as cheating on Takt even for any holdouts in denial who'd say kisses aren't enough (are there even any lol), but maybe not to the degree that Shizuku is hoping for.
She insists on using that Chekhov's condom on him (finally? yeah right...) so we can safely rule out pregnancy with his baby as one of the conditions she's trying to meet. Whatever it is, it's enough to just bang him at least once.
Given the trickling, drip-feed nature of "progress" in this manga, it is highly likely this is as far as they go and the "main event" is for another time, another cycle, in another castle.
Man, this dumpster fire would be 100% more entertaining if they had to deal with the fallout of say, a pregnancy arc. That they're teens will only make the dumpster fire produce finer, thicker smoke for better entertainment. Just because that rarely happens (I know one and that was a fun dumpster fire).
This is an AoT reference and I love it. Even the Japanese readers are meming on this now. Bertolt is at the end of his patience with these two.