Given the uncertainty, the safest approach is to address both possibilities briefly and focus on L'Arc~en~Ciel since it's a more plausible fit with a 20th anniversary around 2014. Then suggest ways to find their music legally. Also, mention that if the user is referring to a different "Arc en Ciel" project, they should verify the correct name and seek information accordingly.

Also, check if there's any 20th-anniversary official releases from Rainbow. If not, maybe it's a fan project. Alternatively, the user might have confused the name. Maybe it's "L'Arc-en-Ciel", which is a famous Japanese rock band that has had anniversaries. If that's the case, perhaps the user meant "L'Arc~en~Ciel 20th Anniversary". Need to verify that.

Need to be clear, avoid assuming incorrect information, and provide helpful, accurate, and legal suggestions.

Yes, L'Arc~en~Ciel is a well-known Japanese band that started in the 90s. A 20th anniversary would be around 2014. They have released compilations, live albums, and maybe digital releases. The user might have misspelled the name. So adjusting the topic to L'Arc~en~Ciel 20th Anniversary would make more sense. Then the content can focus on their 20th anniversary, official releases, and where to legally obtain the MP3s.

I should clarify the band/artist first. If it's Rainbow, formed by Ritchie Blackmore, they had a 20th anniversary in 1983 or 1984, but after that, the band went through changes. Alternatively, maybe it's a Japanese group named Arc-en-Ciel, which isn't as well-known, but there are bands with similar names.