Shenanigans lead to Kurusu catching a cold. Smith is worried that a mutation that enables cross-species transmission could lead to a pandemic.
(This is actually in the episode.)
As Suu has no anatomy, they send her as nursemaid. Everyone gives her (questionable) advice.
If you marry any of them, I'll kill you.
- D
This is the threatening letter Kurusu receives.
To draw out the culprit, he goes on a very public date with Miia. But Mero's "help" causes trouble, and Miia is drawn away by Draco the Dragonewt.
She's not the sender though.