"Oshichi-ya" is a celebration held on the seventh day after a baby's birth. The baby's Shichi-ya and naming ceremony is held on the seventh day after birth, with the day of birth being considered the first day. In the days before medical science was developed, this was a day to celebrate that the baby had been safe and healthy for the first seven days after birth.
In Japanese customs, a baby's name is written on a naming book and displayed in a tokonoma alcove or on a household altar, and family and relatives are invited to celebrate the name and a celebratory meal. The meal includes red rice and whole sea bream. Since mothers are still not fully recovered from childbirth, there is a tendency to keep the celebration simple.

A naming ceremony is a ritual in which the baby's name and the parents' names are written with a brush on Japanese paper or hosho paper and reported to family, relatives, and the birth god.
There are two types of naming certificates: formal ones written on hosho paper and informal ones. The most important thing is the sentiment, so don't be too nervous about it and prepare a naming certificate that suits your taste. Also, in the past, it was common to display naming certificates on a household altar, but nowadays, as few households have such altars, it seems that people often photograph them on the wall or next to the pillow.