Just one kiss - Heero
Just one Hug - Quatre
Just one Moment - Trowa
Just one Night - Duo
Sadly, you might call Serena a whore or so but the only sexual part will be with the Duo one. If I remember right, each one-shot was going to show the readers how Serena acts around each pilot. I don't like Wufei and he doesn't get along with Serena. So Amia might do the 'Just one' theme with her oc and Wufei.
for a hint.
Serena has dated each piloted, other then Wufei, before official getting with Duo. Trowa was her first love when he was No Name on L3. Heero had a thing with her after she lost her gundam's key and he found it. Quatre was her first kiss and she just like kissing the blond pilot. xD Duo was well... She finds him interesting in anyways.
These one-shots, again if I remember right, take place after the OVA. Serena doesn't do the disappearing thingy anymore.
If I'm wrong about the pairings... oh well. I don't really have ocs for Quatre nor Trowa since I pair Serena up with any of the 4. So nah.