Today [ April 16, 2016 (JST)], an official announcement regarding copyright issues have been answered by an official Voltage INC Tumblr account.
Hi Voltage fans,
First, we want to thank you for your dedication, patience, and understanding!
Next, we would like to extend our sincere apologies for the confusion and upset this incident has caused.
This week, an employee at Voltage Inc. was instructed to file DMCA claims against content in violation of our copyright. Because we have not been clear about what is acceptable, internally or externally, our employee did not have accurate guidelines and these takedowns were inconsistent with our previous stance. Many of you had posts removed without warning or explanation.
To prevent this from happening again, we are creating a core company policy regarding acceptable use of Voltage intellectual property. This policy will be effective at all Voltage offices. As soon as it is complete, we will make it available to you as well.
The takedown requests that went out this week are undergoing thorough internal review. There is content, unfortunately, in clear violation of our copyright. This includes fan work featuring background music from one of our apps, as well as posting of paid content in excess of “fair use” such as a collage of official CGs and video showing too much paid-access content. Content that should not have been removed will be restored and the DMCA strike will be automatically retracted. If your content is not restored and you believe it should be, please follow Tumblr’s counter-claim procedures.(According to their policy, the requirement to respond to claims within 10 days is on our side, not yours.)
The Voltage community is a passionate, creative, inclusive, and welcoming place. Seeing your art, stories, theories, and general excitement humbles us and inspires us to create and share our games with you. We hope you continue on this journey with us!
Based on the official answer, any paid contents including music, video and CGs are not allowed to share.
Voltage is creating a core company policy regarding acceptable use of Voltage intellectual property. The company will make it available for all users to read.
I will update more when we get the new policy.