seiko is my UTAU character and you can read more about them on their website: https://utauseiko.neocities.org/

Quick Reference When It Comes To Terms & Conditions For Seiko:

ART

• ok to use any concept art provided on the downloads page. please credit me as mikayuuchann.
• reposts/reprints are forbidden
• commercial use requires permission from me :)
• fanart/fanworks are OK! keep it PG-13 (no overt gore or sexual themes)

VOICEBANK

• you can use seiko for covers, original songs, etc without asking for permission
• contact me for any commercial use of the voicebank (if you want to sell an original song with seiko online, for example)
• dont publicly redistribute the entire voicebank or individual files. exceptions: oto.ini, .frq & prefix map files
• dont use seiko's voicebank in explicit (sexual, grotesque, violent) material. keep it PG-13