Interception Fire is a mechanic in the Valkyria Chronicles series wherein certain units can open fire on a sighted opposing soldier during that soldier's movement phase, allowing units to defend the ground they occupy on an opponent's turn. It is distinct from Counter-Fire, which is a unit's ability to automatically return fire on an opponent who has just attacked them with a firearm but failed to kill them.
Interception fire is automatic and occurs when a soldier moves within the field of view of an enemy unit that can perform it, within a set range. The intercepting unit will open fire on the unit being controlled with their default weapon (they will not use alternative equipment such as grenades), reloading per the capacity limit of their weapon, but continuing to fire on the unit until it either dies, ends its movement phase, or moves out of their range or field of view. Interception fire only takes place in movement mode: enemies do not deliver interception fire if a unit switches to aim mode, though they can finish firing part of their current volley of shots if they started their firing animation before aim mode was activated. Units also cannot take interception fire damage during the animation for ending their current movement phase.
Units are limited to their current field of view, which is 270 degrees for Scouts and 90 degrees for other classes. They will not turn around unless an enemy unit passes fairly close to them, but will turn to continue delivering fire against a unit they have already seen. This behavior can be exploited by having one unit turn around defending opponents and then having another pass by in the direction they were originally facing. Units that are concealed in long grass will not deliver interception fire unless an enemy passes close enough to spot them, at which point they will stand and open fire.
This does not work with tanks, as a tank does not turn its body to deliver interception fire, only its turret, and returns its turret or gun to facing in its default direction at the end of every enemy Movement Phase. Tanks have fixed fire arcs for interception fire, usually 90 degrees to their front but up to 270 degrees for some models. The Medium Imperial Tank even has a rear-facing machine gun. Tanks do have to traverse their guns to deliver interception fire and this is often fairly slow, and so may fail to engage troops passing within their fire arc to their sides.
Interception fire is aimed at the target unit's center of mass (or the "origin bone" of their character model, to be more exact) and the firing unit will not attempt to lead a moving target, meaning approaching at an angle will vastly reduce the number of hits compared to approaching head-on (though they will still take some hits due to the randomization of shots). It cannot achieve critical hits no matter where it hits. Interception fire by the player's units never counts as a Co-Op Attack, even if the units performing it are friends.
Interception fire only targets the unit currently being moved, but can strike other units and will still deal normal damage to them. For example, if a soldier walks behind an ally in an attempt to heal them with Ragnaid, interception fire aimed at the soldier behind will damage the soldier in front.
Enemy infantry have different reactions to interception fire, depending on their AI: This is implemented as enemies simply trying to tank the interception fire as they move to wherever they are going (and frequently dying in the process), while other enemies will tend to stop as soon as they encounter interception fire and attempt to fire on their intended target from where they are standing, or end their movement phase if they cannot.
The AI has a unique ability to avoid interception fire if it does not intend to move a unit before firing, by switching directly from Command Mode to Aim Mode: there is no way for the player to duplicate this.
In Valkyria Chronicles, Scouts, Engineers, Shocktroopers, most Tanks and most Fixed Weapons can perform interception fire, while Snipers and Lancers cannot. Tanks can only perform interception fire with their machine guns. Oddly, the Shamrock cannot perform interception fire with the main weapon of the Gatling turret, despite it being a machine gun.
In Valkyria Chronicles 4, all of the above units can still perform interception fire, and so can Grenadiers and Elite (level 11+) Snipers. Grenadiers and Snipers intercept with special ammunition that has infinite stock and cannot be used for regular attacks (and is generally weaker). Unlike other units, Grenadiers can intercept moving enemies within any ally's field of view. Depending on the mortar equipped, Grenadier interception will either inflict a slow movement status effect on infantry, or completely drain the AP of vehicular enemies caught in the blast.
Grenadiers still count as moving for purposes of interception fire while they are setting up or putting away their launcher, making them very vulnerable during this process.
On the enemy side, Anti-Tank Cannons gain the ability to fire interception fire at vehicles, and there are Boss tanks that have the unique ability to fire interception fire while they are moving on their own turn.
With exceptions to Anti-Tank Cannons, all interception fire is subject to a 0.9x damage multiplier making most weapons deal less damage when intercepting compared to direct attacks and counterattacks.
The duration of the animation of switching to aim mode depends on the weapon wielded, with larger weapons such as Lances taking longer. For units other than Grenadiers, exposure to interception fire can be reduced by selecting ragnaid before entering aim mode, then switch to other weapons while in aim mode.