After the talk with the Asari councilor, you may link up with Admiral Hackett to report. Exit to the CIC and read your new messages. All of people you need to meet are in the Citadel so you should head there next. However, since EDI has gone offline, you have to go to Deck 3 first. Head to the clinic then open the AI Core. After watching EDI take on a new body (she is now available as a squadmate), you're free to check out the ship, modify/upgrade your weapons and gear and purchase other mods/armor. You can also have a talk with Garrus to unlock the Armor-Piercing Ammo upgrade in the Medical Bay.
Once done, head back to the CIC. Talk to Specialist Traynor to learn about a request for assistance from Grissom Academy. There are new star systems to discover added to your galaxy map so make sure to visit them and scan them to gather more war assets. You can also head to the Citadel for now to meet up with the people who sent you messages to your private terminal and start up new sidequests.
During your stay here, there's a whole lot of extra/optional work to do but will help you in your campaign in the long run. This section of will list all the optional stuff you can do and trigger at this point of the game. If the arrangement of the information below is somewhat confusing, you can check out the Sidequests section of this guide to see the convenient list of steps to complete the missions.
You can unlock more stores by checking the Sirta Supplies kiosk in the Hospital and the Spectre Requisition inside the Spectre center in the Embassies. New areas in the Citadel are now accessible via elevator.
You can find a refugee and docking officer arguing. Support one of them to increase your reputation.
You can find a Preacher here. Recover the Pillars of Strength from the Kite's Nest star system. (Refer to the War Assets list of this guide for more information)
Beside the preacher, you'll find a Batarian State Arms kiosk.
You can find Darner Vosque of the Blue Suns in the far corner of the docks. He'll need you to find a way to deal with a turian general named Oraka.
You can find Garrus here as well.
Talk to Ambassador Dominic Osoba near the elevator to unlock the sidequest (Benning: Evidence)
Head to the Spectre office and talk to Jondum Bau to start the sidequest (Citadel: Hanar Diplomat)
If you have received Aria T'Loak's request to help her unite Omega's mercenary bands, then you can enter the C-SEC HQ and talk to Bailey. He will then ask you to visit the C-SEC outpost in the Presidium Commons.
Enter the Spectre headquaters and examine the terminal. From here, you can authorize full pardons for the two engineers that first served the Normandy SR2 (in ME2) as well as enabling tracking of Hanar Embassy.
You can now find Dr. Ravin in the hospital, where you can deliver the advanced medi-gel you acquired from the Cerberus Lab earlier. (Citadel: Alien Medi-Gel Formula)
As you enter the hospital wards, you'll encounter an asari looking for improved biotic amp interfaces. This sidequest will be automatically added to your journal. (Citadel: Biotic Amp Interfaces)
You can also start another sidequest by overhearing a scientist looking for Prototype Components inside the room across the medical wards. (Ismar Frontier: Prototype Components)
You'll find a visitor and receptionist having a discussion. Talking to one of them will increase your Paragon or Renegade status.
On your way to the purgatory, you'll overhear a technician mentioning something about an improved power grid. This will automatically add a sidequest in your journal. (Citadel: Improved Power Grid)
Head inside to find Aria. Approach her to start a conversation. She'll offer help by asking your assistance in uniting the three mercenary bands in Omega under her rule. This will prove a considerable help for your crusade against the Reapers so might as well do it.
Aria: Blood Pack
Aria: Blue Suns
James is also hanging out there. Talk to him to increase your reputation.
The bank counter has the Elkoss Combine Arsenal Supplies kiosk. There's also a Kanala Exports kiosk nearby. Examine it to add it to your ship's procurement list.
There are a couple of civilians near the bank which you can give advice to. Doing so will increase your reputation.
Approach the volus near the bank counter to overhear his conversation. This will open up another sidequest. (Irune: Book of Plenix)
You'll find a salarian and turian businessmen discussing. Warn them about Palaven to earn reputation and update your war asset.
Near the Meridian Place Market, you'll find a salarian talking over the phone. Just overhearing him will start a sidequest. (Citadel: Heating Unit Stabilizers )
In the Meridian Place Market, you'll find a customer bugging a store clerk for a refund. Mediate to increase your reputation.
Aegohr Munitions, Cipritine Armory, Nos Astra Sporting Goods kiosks are available. Interact with them once to add them to your ship's procurement list.
Liara, Joker and EDI are hanging around by the market area. Talk to them to increase your reputation. Liara will also tell you to talk to Barla Von in the bank area.
After talking to Liara, talk to Barla Von. He will ask you to rescue the Shadow Broker forces trapped in the Dranek System.
Head to the apartment area and enter Narl's room. Cooperate with him and you'll earn the allegiance of the Blood Pack after a short scene.
Once you're done in the Citadel, you can now leave and pursue the next available missions.