Why Takamori's been barely getting crumbs I can't remember if it was here or somewhere else but it was pointed out that it's been years since they've had a one on one collab. I mean I voted Gigi to traumatize Mori further but that's besides the point
You probably saw this tweet
They are still close, they just never had a 1 on 1 in a game since then. They still see each other in group collabs and see each other when Kiara is in Japan. It just happens that Kiara refuses to do zatsu collabs, because she thinks those are boring (they are not). The way Kiara approaches collabs is very JP actually, she needs either pre-selected Talking topics and a script (like with Girls talk) or a game. Oh, and it can't be just any game, there has to be a logical reason why she is playing this game with this member. And for the longest time, there were no games where Kiara felt like they are a reason to collab with Calli, because Kiaras brain won't allow to do collabs just for fun (sadly).
But they are still close, Kiara and Calli hang out pretty much every time in Japan. And just the other day, Kiara said about the Takamori panel that doing events with Calli, "feels like coming home"
I don't remember if it was Kiara or Calli who said it but they basically told their audience that they wanted the Takamori shipping to stop because it was beginning to make their friendship really uncomfortable on stream. The yurifags got too obnoxious I'm assuming.
This is actually a common misconception. Takamori did NOT cool down the shipping because Yuri fags got too obnoxious.
Before debut already, since Kiara and Calli were the only ones to meet irl and get close, they decided to use their character lore for some fun dynamics out of the box. They both commonly agreed upon to have this Tsundere - Deredere dynamic that matches their characters.
Kiara was never all that annoyed by the shipping (Calli probably more so) but that was never the reason they laid Takamori down. Its just that they both underestimated how playing that dynamic on stream would play out. Kiara would go wayy too hard and over-act and Calli, trying to keep in character, would steer in the other direction and act extra cold.
As time went on in the first few months, they both noticed that this isn't really working out as they imagined. They stopped because playing into those tropes was getting in the way of them showing off their actual, irl dynamic that they have with each other.
So Kiara dropped the acting love-drunk over Calli act and Calli dropped being so cold or even ignoring Kiara. The way it came to a close might even have been a push from Calli, not Kiara, because Calli herself felt bad treating Kiara like that on stream and was afraid of hurting her feelings by only calling her Kusotori. Calli felt uncomfortable with being so fawned over by Kiara but also having to act cold towards her, contrary to how they act off stream.
Sure, there was bit of overzealous shipping going on, but that one mainly came down to the steep difference in popularity between the two during their first 6 months lets say. Mainly among more casual Deadbeats, Kiara stopped being a streamer and person of her own and just became an accessory for Calli and Callis love interest.
Read some old Takamori fanfics from that time and you will see what I mean. These people clearly have never seen a Kiara stream and just imagine her whole personality off 1 clip.
But the "Shippers would spam their chats whenever they would collab outside of their ship" thing is just a rumour that won't stay dead. Maybe it happened to other Vtuber ships, but it was never an issue that grew out of control for Takamori (it happened but it would not destroy a collab). Even during the peak of Takamori Kiara collabed with other Girls just fine.
Their relationship/friendship did cool off for a solid time in 2021 up to end of that year. It was after Kiara left Japan and came back to Austria, she had a few cries stream about how much she misses Calli. Calli was pretty much her only friend in Holo, she was not yet close to the other Myth girls, and she just felt like she lost that one and only friend. Calli on the other hand did admit to neglecting her and not really responding to her messages during that time and moving on with her life during a members stream (that might have been in 2022 or 2023). I believe feelings of guilt over that drive Calli to be a good and attentive Senpai who is always there for the other girls to this day.