Most Japanese funerals are conducted as a Buddhist ceremony. My sister-in-law was a member of the Christian organization known as Makuya and when she died last week her wishes were to have a Christian ceremony. What's the difference? Well, as a Buddhist ceremony the Buddhist priest does the rituals, uttering words that most people - even the Japanese - can't understand completely. Lots of incense is burned.
In the case of my sister-in-law we held the usual "tsuya" - the wake - on day 1 which was attended by family & friends - friends mainly from her church. Although it was a Christian ceremony some things remained the same. We started off by gathering in a room next to the funeral hall where everyone had a meal. The ceremony consisted of her church members leading the attendees in Christian songs and the elders speaking a few words about her. Per her wishes her casket was surrounded by many, many flowers - not so usual in Japan - but again, this wasn't the typical Japanese funeral. After the ceremony we were back in the room for another meal. Family and friends spent the night there at the funeral parlor - talking into the wee hours and sleeping on futons (I went back to the house - this is one part of the ritual I prefer not to observe).
Day two was another short ceremony with more songs, bible reading, and speeches from a few people who knew her & wanted to say some final words. From there we went to the crematorium where we said our final farewells before the coffin was rolled into the flames. While we waited for the cremation to be completed we gathered in a room for a light lunch. The cremation took about 1 1/2 hours. Once the cremation was completed we gathered around the remains for the ritual picking of the bones to be placed into the urn. A few bones are all that are left after a cremation - there really aren't ashes in the sense that we think of ashes - the bones are brittle & when pressed into the urn become what we think of as ashes. Bones are picked up using chopsticks and passed to the next person's chopsticks a few times before being placed into the urn. This is why it is considered extremely bad practice to pass food from chopsticks to chopsticks - this ritual is for the bones of the deceased - not for food.
Once the bones were placed into the urn we all got onto the bus that had been provided by the funeral parlor and returned to a final short service - this was the very last of the farewells. From there the ashes were taken home where they will stay until placed into her final resting place.
All in all, not so much difference between the two types of ceremony - Buddhist or Christian - but the Christian one is a bit simpler & there were family members there who felt that this could be the way for them too when their time comes even though my sister-in-law was the only one in the family who belonged to this particular religious sect.
If you are interested in learning more about how funerals are conducted in Japan - or weddings - or more - there are plenty of websites - do a bit of a search & you'll most likely come up with information overload.