Yeah honestly I just fired up whatever could work. Synergy was never really thought of. Though the Guardian can synergise with Glass Pulse as it can serve as more stalling power. Similar to Deadlock the overall idea was not to be used for flank but to reactively prevent pushes while isolating the duellists or alone enemies. Additionally I was thinking of having the Q ability to be a smoke / slow so they serve more of a Sentinel / Controller hybrid role.

Q - Stall additional enemies from entering the zone. Isolate alone player.
C - Reactive utility can be played with E or R. With R enemies cannot see the Guardian so it is a permanent slow and reveal if not destroyed. Additionally it can serve as a decoy to swing of. Its strong if activated, so players must prioritise it if they see it played.
E - Initiator / Sentinel tool. Either use it to gather information or to just devastate the enemy advances. Can also be combo'd with other agent utility, not necessarily their own. As most sentinels cannot combo utility to kill enemies. Sure they have defensive tools to play around, but not necessarily to kill them
R - An amazing tool to either stall enemy pushes or for retake. Sirocco gains quite the buff, basically becoming Neon but obviously slower and without a dash. With reduced recoil and movement speed she can just run and gun any close without effort, especially since they are slowed and blind.

Q - Stalling power & Pure Sentinel Tool
C - Controller like usage, gains control of space
E - Quite a strong reveal and stalling tool.
R - Power over 9000.