For me it took more than 4 months for me to receive the visa after I have sent the company (I was a direct hire) the documents they needed.
A visa approval taking a longer time than usual depends on a lot of factors such as:
1. Internal processes in the commpany your brother applied to.
2. When was the NOC issued / When did your brother leave Qatar?
3. What were the circumstances of leaving? end of contract or termination?
4. Where is the intended work location? You mentioned a Japanese company. If it is a Japanese company in Ras Laffan then it would require additional security checks.
5. Company hiring your brother. There may be previously pending visa application being processed for the company.
6. Nationality. There are additional checks for certain nationalities.

Your brother just have to be patient. As I've said I waited more than 4 months - I submitted all my documents in January 200X. At end of February, they sent me my contract for signature and assured me they are processing the visa. They sent me the visa at mid-May. And I received the e-ticket on June 1 for a June 2 flight to Doha.