It was part of an album from August 2019 with most of Shade's music from back then, "Azur Lane: Special Soundtrack" with this track being called "Forgotten Hero" (the Air Raid Drills with Essex theme is called "For Blue Freedom"). The "Mystic Mirrorheart" track is from the same album (where it's called "Mirrored Heart (Ego)" instead). There are a lot of currently unused tracks on that album, though the fact they've added 2 of them recently probably implies the rest are coming, including a remix of Iris of Light and Dark's normal battle theme (the normal version being called "Like the Sacred White Lily", while the remix is called "Iron Blood Lily"). You can find that remix by searching the japanese track name: "アイアンブラッド・リリィ" (a channel that's uploaded some of the tracks from the album 2 months ago should appear as one of the top results, though there are other unused tracks not uploaded by them). There are 7 unused tracks remaining... "Cutting Down the Sakura Empire Blade", "Advance! Knights of the Sea", "Operation to Destroy Large Weapons", "Dream of a Saint", "Conquer the Ocean", "Old War" and the one mentioned above, "Iron Blood Lily".
No way. They remixed the OST of Air Raids with Essex, eh?
It was part of an album from August 2019 with most of Shade's music from back then, "Azur Lane: Special Soundtrack" with this track being called "Forgotten Hero" (the Air Raid Drills with Essex theme is called "For Blue Freedom"). The "Mystic Mirrorheart" track is from the same album (where it's called "Mirrored Heart (Ego)" instead). There are a lot of currently unused tracks on that album, though the fact they've added 2 of them recently probably implies the rest are coming, including a remix of Iris of Light and Dark's normal battle theme (the normal version being called "Like the Sacred White Lily", while the remix is called "Iron Blood Lily"). You can find that remix by searching the japanese track name: "アイアンブラッド・リリィ" (a channel that's uploaded some of the tracks from the album 2 months ago should appear as one of the top results, though there are other unused tracks not uploaded by them).
There are 7 unused tracks remaining... "Cutting Down the Sakura Empire Blade", "Advance! Knights of the Sea", "Operation to Destroy Large Weapons", "Dream of a Saint", "Conquer the Ocean", "Old War" and the one mentioned above, "Iron Blood Lily".