Operation Thaelvak

The conquest of Falkeos had left nearby Diab colonies open to Pact invasions; this was compounded by Zaretian and Rathakern attacks elsewhere, which pulled a number of Diab troops away from the foothold. This prompted the Diabs to evacuate nearby colonies and dig in with their available forces. Emboldened, Imperial Command began planning for its next move mere days after the Falkeos campaign had concluded. The offensive, codenamed Keros, would have Warlord forces engage the Diabs along three prongs. The central prong would be manned chiefly by Magello and Skrey, and intended to tie down Diab manpower. The right prong, known as south, would be led by the 14th and 277th armadas while the left, known as north, was spearheaded by the 355th and Commandant Tor. North and south were to push along the central prong's flanks and gradually sweep around and cut off the defenders. As well as pushing the foothold deeper into Diab space, this would make the foothold less dependent on outside assistance in terms of resources, as they would have more land to exploit.

While preparations were still underway, the Aeverians initiated Operation Burning Lance, the sheer size of which caught many in Imperial Command off guard. It was proposed that the Repzork halt their current plans in order to support the Monarchy, but this was rejected by the Marshal's Council, who aimed to prevent the Diabs or Karahotdoum from supporting the Aeveria by keeping them on the defensive. The 843rd, which was already stationed in Aeverian territory alongside the Necraal, would focus their efforts on diverting Aeverian resources away from the offensive with limited-scale attacks. Imperial Command would continue to monitor the Aeveria's progress, but the Zaretian's rapid response and the subsequent halt of Peacekeeper forces restored some confidence that the Zaretians could hold their ground, at least for the moment.

The Pact's buildup did not go entirely unnoticed by Diab Valkyries, who had been sent into the foothold to act as scouts. Though the Peacekeepers did not know where the Warlords would attack, they believed that an offensive would be sooner rather than later, and used what time they had to prepare. With the colonies having been evacuated, the Diabs focused their efforts on major colonies, such as major population and industrial centers, while leaving smaller units stationed at low-priority systems to slow down the Pact's advance. A large number of reserves were withheld for when the offensive began; they were to be deployed wherever they were needed.

The Keros Offensive officially began with all three prongs simultaneously attacking. The Diab's outermost defenses were shattered, but had fought to the last man, buying precious time. Pact forces made substantial gains in the following months, but had underestimated the number and tenacity of the defenders, which robbed the south and central prongs of some of the momentum that Imperial Command had expected, the central front gradually slowing to a crawl. The north front was the exception, the 14th and 277th advancing deep into enemy territory through a mixture of strategy and unrelenting force. The Diabs were quick to respond, sending the bulk of their reserves to engage the north prong, though they would be unable to halt the north's advance.

Battle of Embaelos
The Diab colony of Embaelos had been one of Falkeos' suppliers of manpower and equipment. Since Falkeos' fall, Embaelos had been repurposed as a forward command center for the Diab's fight against the Northern prong throughout the Keros offensive. Imperial Command has made the capture of Embaelos a priority objective for the Keros Offensive, and the North prong had been steadily advancing towards the colony since the offensive had begun. Knowing the planet would be attacked, the Diabs planned to turn Embaelos into a trap. Allied command diverted troops initially intended for the central and southern fronts to a system near Embaelos. They were to maintain position until after the Repzork had begun the attack, and were to isolate and cripple either the 14th's or 277th's command fleet, eliminating the fleet's commanding officers in the process. Unbeknownst to the Diabs, the Repzork, knowing that Embaelos would be heavily fortified but unaware of the Diab's plans, devised a ruse. The 277th would launch a feint against the Diabs and would then, after a brief engagement, withdraw, intending to draw out the defenders. Elements of the 14th would then sweep in and attack the Diab's exposed flanks. To make the trap more convincing, the 277th's command fleet was to be included in the attack.

The Repzork began the attack with standard tactics, giving the impression that a full invasion force had come, but the Diabs quickly took notice of the unusually small size of the force. Some concluded that it had to be a trap, but with the 277th's command fleet taking part in the attack, others believed that the Repzork were either unaware of the planet's strategic significance or had simply underestimated the defenses. After a brief period of intense fighting, the 277th began to pull back, but before it could do so, the Diabs sprung the trap, and their reserves appeared behind the invaders. Now severely outnumbered, the 277th alerted the 14th to their situation. The 14th then arrived and caught some of the Diabs by surprise.

As the 14th fought their way towards the 277th, the 277th's flagship was temporarily disabled and boarded by several waves of Diab shock troopers tasked with either capturing or killing Star Marshal Vilotr and Field Marshal Likana. An intense battle broke out throughout the ship, during which Marshal Likana donned her personal battlesuit and fought alongside her troops. She killed many of the attackers before her battlesuit was rendered inoperable after repeated shots to the legs. The field marshal continued to fight, but was incapacitated soon after, and had to be dragged away by her personal entourage before the Diabs could apprehend her.

Before the Diabs could eliminate the flagship, additional Repzork troops began to surge into the system in vast numbers; the attack had drawn the attention of all available elements of the 14th and 277th, who had been ordered to the system by Star Marshal Kiryusa Luok. The Diabs were repelled, and the 277th's command fleet subsequently fled the system, returning to the foothold for repairs. The battle nevertheless continued, the Repzork intent on seeking vengeance and claiming the planet. After a bitter engagement, Embaelos fell to Repzork forces.

Though the Diabs had failed in their objectives, the battle had nonetheless checked the rapid advance of the northern prong, especially in regards to the 277th. Marshal Likana would be hospitalized for several months, during which command of the 277th's ground forces fell upon her second-in-command, General Ezanfi Dugoro. Portions of the 277th, most notably the command fleet, were recalled to the mainland, with Marshal Vilotr and General Ezanfi temporarily taking direct command of one of the 277th's attack fleets. The Keros Offensive would continue, but the northern prong would never regain the initiative it had prior to Embaelos.

With the northern salient contained, the Diabs turned their attention towards the southern salient. Having been reinforced by troops from both the southern and central fronts, the Diabs initiated Operation Iron Gauntlet, which aimed to reclaim the salient, cripple the 14th and 355th armadas, and open a passage to Falkeos, and ultimately, to Baltreos. The Peacekeepers focused the bulk of their troops at the salient's base, intending to cut it off from the foothold. Though heavily fortified, the salient's defenses were shattered in the assault before the Pact could respond, and the salient was severed. As the Diabs advanced down the salient, smaller attacks were launched at other portions of the area, though these assaults made little progress. As the 14th armada moved to meet the main Diab force, reinforcements from the foothold arrived into the sector, though they were cut off by Peacekeeper fleets until a daring attack by the 57th Magellan fleet caused a break through, allowing the Warlords to stabilize the front. Repzork forces made heavy use of crystal munitions at this point in the battle, particularly during ground engagements, where crystal-infused artillery shells, bombs, and grenades made traditional Diab tactics risky or impossible. After several more weeks of fighting, the Diabs were finally repelled by the sudden arrival of the 277th, which had recently completed replenishment.

Though repelled from the salient, the Diabs continued to attack the sector in several locations, waging a battle of attrition costly to both sides. Systems changed hands often, sometimes several times in only the span of one or two months, but neither side made substantial gains against the the for next seven months.