The badge was reportedly available to around 500 female members of staff, with the intention of helping staff recognise when colleagues with their period might need extra help or a break.
Seiri-chan, a character with a heart-shaped face and big red lips, has become something of a hit in recent months in Japan, a nation where public talk of women's bodies and periods is often taboo.
The brainchild of manga artist Ken Koyama, Seiri chan features in the popular comic Little Miss P – alongside catchily-named characters such as Little Miss PMS and Mr Virginity – and even starred in her own live-action comedy released this month.
The workplace has long been a challenging place for Japanese women, with the nation often lagging far behind many other developed countries in terms of gender equality.
Female workers are often exposed to deeply traditional gender expectations, as reflected by Japanese women earlier this month demanding the right to wear glasses to work, amid reports that some employers had banned them.
Earlier this year, more than 21,000 people also signed a high profile online petition calling for Japanese companies to stop forcing female staff to wear high heels to work.