Here Andou calls Oshida Ruka, which seems to be Oshida's first name based on the finale website's character pic file. On the other note, it also seems that Andou's first name is Rena.

DAS58 said:

Here Andou calls Oshida Ruka, which seems to be Oshida's first name based on the finale website's character pic file. On the other note, it also seems that Andou's first name is Rena.

Ah, that's good to know. I also double-checked with Pixivpedia, and it's also there.

However it's better to keep the character tags is is, but I did update their wikis, just like the other characters whose full names are known but not used.