Intellectual property attorney, if a person who was assigned the copyright made a similar song, is it copyright infringement?

Even where the entirety of the economic rights of copyright has been assigned, the Copyright Act presumes that the right to produce derivative works, which may harm the original form of the original work, is reserved to the original copyright holder.

Therefore, even if you were assigned the economic rights of copyright, if plagiarism occurred in a derivative work, it may be recognized as an infringement of copyright.

However, if the parties agree by special agreement to also assign the right to produce derivative works and the like, that agreement is, of course, valid.

If you had no separate special agreement, among the author's economic rights of copyright, the right to produce derivative works and the right to produce compilation works may be deemed not to have been assigned to the other party.

Therefore, the rights to a derivative work can be regarded as remaining reserved to the original author.

In such a case, the most ideal approach is to reach an amicable settlement with the original author through the mediation of an intellectual property attorney.

However, if a settlement is not reached well, the author can exercise the right to produce derivative works against the other party even after the assignment.

If substantial similarity is recognized through a legal determination, there is a high possibility that it will be regarded as an infringement of the original author's economic rights of copyright or moral rights of the author.

Even where a derivative work is recognized as having added new creativity to the original work, it can amount to producing a derivative work of the work without the original author's permission.

Therefore, even in a situation where you have been assigned the economic rights of copyright, producing a derivative work requires a detailed legal review, so it is advisable to seek advice from an intellectual property attorney.