Question: Who did the QRA prioritize trying to intercept?

Context paragraphs:
LIM-49 Nike Zeus: Nike Zeus was an anti-ballistic missile (ABM) system developed by the US Army during the late 1950s and early 1960s, designed to destroy Soviet intercontinental ballistic missile warheads before they could hit targets in the United States.  It was designed by Bell's Nike team, and was initially based on the earlier Nike Hercules anti-aircraft missile.  The original Zeus A, given the tri-service identifier XLIM-49, was designed to intercept warheads in the upper atmosphere, mounting a 25 kiloton W31 nuclear warhead.  During development, the concept changed to protect a much larger area and intercept the warheads at higher altitudes.  This required the missile to be greatly enlarged into the totally new design, Zeus B, mounting a 400 kiloton W50 warhead.  In several successful tests, the B model proved itself able to intercept warheads, and even satellites.

Maidenhead Locator System: The Maidenhead Locator System also QTH or QRA grid system (deprecated) is a geographic co-ordinate system used by amateur radio operators to succinctly describe their locations.  Its purpose is to be concise, accurate and robust in the face of interference and adverse transmission conditions.  The Maidenhead Locator System can describe locations anywhere in the world, and replaced the previous QRA locator system which was limited to European contacts.

Fighter units of the Japan Air Self-Defense Force: Fighter units of the Japan Air Self-Defense Force are squadrons of fighter aircraft dedicated to the defense of Japan.  One of their main activities is providing Quick Reaction Alert intercepts to Chinese and Russian aircraft nearing or violating Japanese airspace.  In 2016 Japan Air Self-Defense Force (JASDF) aircraft launched 851 times to intercept Chinese aircraft and 301 times in response to Russian aircraft.

Quantile regression averaging: Quantile Regression Averaging (QRA) is a forecast combination approach to the computation of prediction intervals.  It involves applying quantile regression to the point forecasts of a small number of individual forecasting models or experts.  It has been introduced in 2014 by Jakub Nowotarski and Rafał Weron and originally used for probabilistic forecasting of electricity prices and loads.  Despite its simplicity it has been found to perform extremely well in practice - the top two performing teams in the "price track" of the Global Energy Forecasting Competition (GEFCom2014) used variants of QRA.

Intercept method: The intercept method, also known as Marcq St. Hilaire method, is an astronomical navigation method of calculating an observer's position on earth.  It was originally called the "azimuth intercept" method because the process involves drawing a line which intercepts the azimuth line.  This name was shortened to "intercept" method and the "intercept distance" was shortened to 'intercept'.

Quick Reaction Alert: Quick Reaction Alert, known colloquially as QRA, is state of readiness and "modus operandi" of air defence maintained at all hours of the day by NATO, mainly involving the Royal Air Force (RAF).

Y-intercept: In analytic geometry, using the common convention that the horizontal axis represents a variable "x" and the vertical axis represents a variable "y", a "y"-intercept or vertical intercept is a point where the graph of a function or relation intersects the "y"-axis of the coordinate system.  As such, these points satisfy "x" = 0.

Second-order intercept point: The Second Order Intercept Point, also known as the SOI, IP2, or IIP2 (Input Intercept Point), is a measure of linearity that quantifies the second-order distortion generated by nonlinear systems and devices.  Examples of frequently used devices that are concerned with this measure are amplifiers and mixers.  It is related to the third-order intercept point, which is generally used for quantifying degree of nonlinearity of a nonlinear system or it can also be used to estimate the nonlinear products present at the output of such a system.

QRA locator: The QRA locator, also called QTH locator in some publications, is an obsolete geographic coordinate system used by amateur radio operators in Europe before the introduction of the Maidenhead Locator System.  As a radio transmitter or receiver location system the QRA locator is considered defunct, but may be found in many older documents.

Third-order intercept point: In telecommunications, a third-order intercept point (IP or TOI) is a measure for weakly nonlinear systems and devices, for example receivers, linear amplifiers and mixers.  It is based on the idea that the device nonlinearity can be modeled using a low-order polynomial, derived by means of Taylor series expansion.  The third-order intercept point relates nonlinear products caused by the third-order nonlinear term to the linearly amplified signal, in contrast to the second-order intercept point that uses second-order terms.

Supporting paragraphs: Fighter units of the Japan Air Self-Defense Force Quick Reaction Alert
Answer: Chinese and Russian aircraft