Seiji watched Minto's ballet recitals when he was younger. However, he later became too busy attending his private school and getting involved in the corporate world to pay any attention to his younger sister anymore, causing the two to grow apart.
Tokyo Mew Mew
In episode 9 of Tokyo Mew Mew, Ichigo made a plan to have Seiji attend one of Minto's ballet recitals. He initially didn't want to, until she saw flowers at a shop that were the same as those he'd given to Minto when they were young. He then arrived at her recital, when a black swan chimera with the spirit of a ballerina attacked him. He tried to protect Minto, but was knocked out. Minto transformed and defeated the chimera anima in the end before her recital, and Seiji told her she was still important to him. He gave her the flowers and watched her ballet recital.
- Mew Mew Power - Sergio Bucksworth
- Mew Mew Amiche Vincenti (Italian) - Sergio Aizawa
- Dong Jing Mao Mao (Mandarin) - Shì-Sī LánZé
- Berry Berry Mew Mew (Korean) - Minseo Ju
- Seiji's english voice actor, Jason Anthony Griffith, is famous for voicing Sonic and Shadow the Hedgehog from Sega's famous Sonic The Hegdehog series. He provided their voices in the Sonic X anime, which was dubbed by 4Kids Entertainment like Mew Mew Power was.
- He was described by Retasu and Ichigo to be tall and handsome.