One of the most map-dependent COs in the game, Javier is a Green Earth CO who only truly shines where he can use Comm. Towers.
Playing as Javier
Javier relies on maps having Comm. Towers to be effective. Javier alone, without towers, is one of the worst CO choices in the game. With even one Tower, however, Javier becomes a force to be reckoned with, having units on par with those of Von Bolt. As such, Javier excels in areas similar to Von Bolt: smaller maps that allow for his Tanks to cover a lot of ground without downtime. While his defense against Indirect attackers will help reduce some of the sting from Artillery fire, they can still very much deal significant damage to his units, so one should not rely on the Indirect defense to save units. Javier will want to use his superior units to bully other COs and build his CO Power bar, as his CO Power, while inexpensive, is quite strong.
With one Tower, Tower Shield allows Javier's units to be on par with Kanbei's for a turn. Enemies will find it difficult to retaliate against an attacking Javier with Tower Shield enabled, typically taking more damage on counterattack in otherwise even unit match ups. Tower Shield will also render Javier's units incredibly resilient to Indirect fire, with Full HP hostile Artillery and Rockets struggling to deal any significant damage to most any of Javier's units. Tower Shield is generally a better power to use over Tower of Power, as Javier will only see an additional 10% increased offense and defense on the latter power, for double the cost. The only time it would be advisable to use Tower of Power is if the enemy has a massive Indirect presence, as with even one Tower, all of Javier's units are completely invulnerable to indirect fire for the duration of the power. Given Javier's presence, however, large groups of enemy Indirect units will be relatively rare.
Playing against Javier
Javier is generally considered a very weak CO when he has no Comm Towers. If the map permits, denying Javier the ability to capture a Comm. Tower for as long as possible can severely hinder him. If Indirect Combat units would prove useful in hindering his ability to Capture Towers, do not hesitate to use them to your advantage; even against 20% extra defense, Artillery are still capable of dealing considerable damage to light units, but should not be overused. Should it become too costly to delay the capturing of his Tower, pulling back is advised, as if he captures the Tower with a lot of damaged targets in the vicinity, he is capable of mopping up quite well.
Tower Shield will be a constant threat throughout the whole game, as it provides a lot of stats to all of Javier's units for a low cost to use. Similar unit match ups should be avoided when Javier has Tower Shield active as, even on the receiving end of an attack, Javier will likely come out ahead of his attackers. Damage will have to be maximized when Tower Shield is not active, which may be difficult in the Mid Game, as he will likely be able to activate it almost every other turn for a short while, before the repeated use begins to heavily slow his CO Power build rate. Above all else, do not let Javier gain control of more than one Comm Tower if at all possible, as Javier with two or more Comm Towers can easily overpower most COs with the Kanbei-esque stats he will get, without the increased unit costs.