Anime about a guy who can play the guitar really well but doesn't know how

Question

I saw an anime on Adult Swim, probably between 2002-2005. It might have been the first episode. But the main character has amnesia or had his memory wiped. He was carrying an acoustic guitar and someone on the street says "Do you play?" and he says no and then plays a really intricate riff and the guy replies "Lying is bad karma, man" and it's obvious the main character doesn't know how or why he can play guitar.

Please know that my quotes are probably paraphrasing the real dialogue.

The anime was in Japanese style but the audio was in English. Also, it was not Phineas and Ferb, I'm familiar with that show.

Answer 1

Android Kikaider: The Animation

Dr. Kohmyoji creates Jiro (Kikaider) but an explosion occurs. When Dr Kohmyoji's kids, Mitsuko and Masaru, their father was nowhere to be found, Jiro wandering aimlessly in a remote area eventually meets Mitsuko. Mitsuko teaches Jiro to go into his robot form and about the GEMINI system inside him. The two grow closer together but the relationship development halts when a mysterious flute playing causes Jiro to attack Mitsuko, which causes her to believe he is a mad machine. Jiro inevitably leaves Mitsuko and Masaru in fear of being destroyed. Mitsuko then hires Hanpei Hattori and his apprentice Etsuko Sarutobi to find Jiro and bring him home. Throughout the story, Jiro encounters robots and learns more about Professor Gill and the evil organization DARK. A reoccurring android named Hakaider causes Jiro out of control by whistling (similar to Gill's flute). The more Mitsuko encounters Jiro the more she falls in love with him. When Mitsuko and Jiro reunite, they search for Mistuko's mother who is revealed to be in love with Professor Gill but could not bare the pain of being away from her children and gives them the location to Professor Gill's headquarters right before she killed herself. After they discover the location, Jiro attempts to fight Hakaider alone and also discovers the brain inside Hakaider's head is that of Dr. Kohmyoji's. Dr. Kohmyoji overtakes Hakaider's body before Hakaider could destroy it and infiltrates the headquarters. Once Professor Gill discovers Dr. Kohmyoji is in control he sends his robots to attack them. Jiro was able to give the brain to Hanpei in order to put it back into Dr. Kohmyoji's body. Professor Gill attempts to control Jiro with his flute, but Jiro to is able to overcome it. Hakaider then attempts to kill Professor Gill for betraying him and destroys the place along with Gill. Hanpei, Mitsuko and Etsuko able to escape, but didn't see Jiro escape with them. In the end, Mitsuko has hope that Jiro will return to them.

Episode 3 to be exact, "Stray Sheep"

At 10:46 the other guitar player says "You shouldn't lie like that, it's bad karma!"

Answer 2

In the Phineas and Ferb science fantasy cartoon TV show, the season 1 episode “Dude, We're Getting the Band Back Together” (linked description on Phineas and Ferb Wikia, WIKIA WARNING), the protagonists convince a three-man rock band Love Händel who had broken up to play music again. They meet the singer guitarist, then the bass player.

The climax of the episode is when they convince the drummer, Swampy, to return. Swampy insists that he has quit playing music because he has lost his sense of rhythm. However, Phineas and Ferb point out the signs, obvious to both them and the viewer, that Swampy is wrong, and he still has a great musical talent and should play the drum again.

This much matches the description in your question well. The conflict is, this is definitely not an animé show, not even animé influenced, but an American style cartoon TV-show. It was also playing on Disney channel, so it's unlikely to have ever appeared on Adult Swim, the channel owned by the competitor Cartoon Network.