Based on the credits on POCX-1001 to "M.MIKADONOSHIZUKA (T.S.)" and "Mari MIKADONOSHIZUKA (T.S.'s another name)," it seems to me that this is an alias of Tadashi Sawashita, for whom Mikadonoshizuka exclusively wrote lyrics.
Bonus points: Sawashita wrote music and lyrics for the ending theme of Wing of Alnam as "T.S.":
