yeah I think it's Hilchryme since I received their debut album Recital on Fri
In the CD sleeves of the album , all the lyrics on Recital were written by TOC while all music were composed by DJ KATSU
So yeah I think it's them behind Naiyou no Nai Tegami
NEWS better do a good job in it

. If not , I write into Universal Japan & ask Hilchryme to release their own version of Naiyou no Nai Tegami as their next single or as an album track in their 2nd album hahahaha