I would consult the gaijinpot forums on this matter because I know for a fact I've seen it discussed there before.

Also, just an fyi but not sure what kind of pardon or where your friend is getting it from, but federal pardons (in the US) do not expunge your record, you are still legally bound (though I guess it is up to you...) to say you where convicted even after pardoned.

i would have your friend talk to an english speaking immigration lawyer before coming here.

keep in mind that if you're denied at the port of entry it can cause you further problems the next time you try to come in. and in this case since your friend will have admitted to having a criminal record, your friend will never have a chance of getting into japan again.

Roughly speaking, a non-Japanese national who falls under any of the followings is denied landing on Japan.
(These are some examples, and not strictly true to the Act.)
- You have been sentenced to imprisonment for one year or more, and the sentence has become final.
(Exception: You have been sentenced on the charge of a political offense.)
- You have been sentenced to any penalty (regardless of the length of the term or the amount of the fine or so) on the charge of violating any law or regulation relating to the control of narcotics, marijuana, opium, stimulants or psychotropic substances, and the sentence has become final.
- You have been sentenced to any penalty (regardless of the length of the term or the amount of the fine or so) on the charge of violating any law or regulation for your participation in a riot in relation to an event such as Olympic Games and G8 Summit, and the sentence has become final, and you are likely to repeat such a deed in a public area of Japan in or near which such an event is held.
- You illegally possess against laws of Japan any narcotics or psychotropic substances, or marijuana, or poppy, opium or poppy plants, or stimulants, or raw materials used to make stimulants, or apparatus used for smoking or eating opium.
- You have engaged in prostitution, or intermediation or solicitation of prostitutes for other persons, or provision of a place for prostitution, or any other business directly connected to prostitution.
(Exception: You have engaged in the business under the control of another due to trafficking in persons).
- You have committed trafficking in persons, or incited or aided another to commit it.
- You illegally possess against laws of Japan firearms, swords or other such weapons, or explosives.

If a fact is found that a non-Japanese national has got permission to land on Japan, by deceit or other wrongful means, as not falling under the conditions for denial of landing, then his/her status of residence may be revoked; and if that's been revoked, he/she may be deported from Japan.
Deported from Japan in that way, he/she will be denied landing for 5 years if he/she has not previously been deported from Japan or departed from Japan, for 10 years if he/she has previously been so.