It seems that one's impression of this church is highly dependent on whether the person gets to see its interior. The church is closed when there are weddings taking place, and it is apparently a very popular wedding venue.
The exterior is what you see in the photos, it's different but does not make a huge impression. However, the inside is extremely beautiful and unique. Layers of light pass through the windows, and vines grow on the side of the stone wall with water trickling down into a small stream that flows through the inside of the church. All you hear is the water flowing. It was so serene.
The pews and altar are made of wood for the location, and look fluid and modern.
Photos are not allowed but it does not hurt anyone to put down the phone or camera and just take in the surroundings.
I think the website could improve by setting the times when the church is open for visits. Until they do that, be prepared. If you happen to catch it when it's open, you are very lucky. Just treat it as one of those things that happen by chance and you won't be as disappointed.
I walked there from Harunire Terrace. After passing the bus top, it's uphill on the left. Google map said 5 minutes. It's more like 15 minutes. I went on a weekday at around 3:30pm. I was the last person they allowed in as they closed the church at 4pm for a wedding. I was very lucky. There was only one other person. The staff then offered to take us to the small museum in the basement, where photos are allowed.
It was a wonderful experience.