Arisaka type 99 7.7mm
Your gun is definitely missing part of the rear sight (the sliding part that goes up the ladder), and has had the stock "sporterized" (trimmed down from the military stock to save weight).
The gun is a variant of the mauser design, but retains the cock on closing feature of early mausers. The 7.7mm round was designed to replace the earlier 6.5mm round, to provide more power. It is ballistically identical to the .303 British round in bullet size and speed, but the cases are quite different, the .303 being rimmed and the 7.7mm being rimless.
The ground on part of the receiver used to have the "mum" on it. Not a "sun" as suggested, it was the chrysanthemum (flower), and was the symbol of the Japanese Emperor. After the Japanese surrender, large numbers of Arisakas were turned over to US forces, and the "mum" was ground off, saveing "face".
Arisakas with intact "mums" indicate battlefield pick up, a ground mum indicates a rifle that was surrendered.
Reloading the 7.7mm is possible, and the most practical way to go. Dies can be found, and even new cases. Cases can also be made from .30-06 brass. New made ammo for the 7.7mm can also be found, but it is not as cheap as more common military surplus calibers. Although the sights are not as good as some military rifles, and trigger pulls range from fair to poor, some of these rifles are suprisingly accurate shooters, once you get past the less than stellar features.
One odd feature of the Arisaka is the safety. It is the large knob at the rear of the bolt, and requires a push in and turn to put the rifle on safe. With a little practice it can be released very quietly, something a deer hunter may value.
There will be markings on the left side of the reciever, after the serial number, which can tell you which arsenal made your rifle, with a little research. Post a good pic, someone here might know more.
If you have some original Japanese 7.7mm ammo, I would recommend not shooting it, as the ammo has proven notoriously unreliable after so much time, and is very scarce, making it worth more as a collector's item than as usable ammunition. You should take your rifle to a good gunsmith and have the headspace checked before trying to shoot it with any ammo, just for safety's sake.