Spoiler
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In the novel "Finder no Raikun", Fei Long tracked Yoh down and asked him to kill Yan (Yan was beginning to rise back up in power with another gang and was planning to take out FeiLong). Yoh agreed to do it to make up for his earlier betrayal. It turned out to be "mercy killing" because Yan was pretty much gone already-- his mind having been destroyed by a heavy drug usage.
Yoh still killed him slowly though.
In Fei Long's novel finder no rakuin his brother does make an appearance. But I'm not sure if he'll be appearing in the manga again anytime soon.
Is Feilongs brother alive? If he is anyone think he'll make another appearance in the next update?