As you indicated by the tags you selected, Hong Kong and The Philippines, firstly, you have to comply with appropriate rules and regulations when you exit Hong Kong, and secondly, deal with the laws and regulations of The Philippines.
As a preface, the Wikipedia summary of legal issues in Hong Kong:
In Hong Kong, airsoft guns are considered toys as long as they are not able to be fired with a muzzle energy above 2 joules of kinetic energy, above which they are considered as a firearm and need registration, and possession of an unregistered firearm is illegal. Under the Section 13 of Cap 238 Firearms and Ammunition Ordinance of the Hong Kong Law, unrestricted use of firearms and ammunition requires a license. Those found in possession without a license could be fined HKD$100,000 and be imprisoned for up to 14 years.
Airsoft guns in Hong Kong is not required to have an orange tip. However, public possession or exposure of airsoft gun is not recommended by the police department in Hong Kong, as it is difficult to identify whether it is a real firearm or not. It is also not required to obtain a licence to sell an airsoft gun in Hong Kong.
Now, departure: for reference, let's use Hong Kong Airlines (you'd have to consult those of your specific carrier). For obvious reasons, carry-on baggage is out: you are not able to have a gun, real or realistic, in the cabin with you. It would have to be in checked baggage, as described in Restricted Articles:
Category 1. Guns, firearms and other devices that discharge projectiles. Devices designed to cause serious injury by discharging a projectile, or capable of being mistaken for such devices, including:
- firearms of all types, including pistols, revolvers, rifles, shotguns;
- toy guns, replicas and imitation firearms capable of being mistaken for real weapons, such as gun lighters;
- component parts of firearms (excluding telescopic sights);
- compressed air and CO2 guns, including pistols, pellet guns, rifles and ball bearing guns;
- signal flare pistols and starter pistols;
- bows, cross bows and arrows;
- harpoon guns and spear guns;
- slingshots and catapults.
Your next challenge is returning to The Philippines. On May 29, 2013, President Benigno S. Aquino III, signed into law, Republic Act. No. 10591: “Comprehensive Firearms and Ammunition Regulation Act." Imitation firearms are included in the articles that require import clearance.
The Philippine National Police (PNP) Firearms and Explosives Office (FEO)
gives the step-by-step proces, and online applications to expedite it. In advance of your travels, you may also want to contact the office directly by phone at (632) 723-0401 loc. 4588 or by email to email@example.com
The Philippine Bureau of Customs includes replica and imitation firearms among the Regulated Articles which must be declared and appropriate procedures and permissions completed prior to arrival at Customs and Immigration.