Is Full Metal Panic! The Second Raid Episode 00 hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV Special · 2005 · 1 episodes · PG-13 - Teens 13 or older
Mecha, Military
Sousuke, Kurz, and Melissa are deployed to the Republic of Manistan in Central Asia to eradicate a growing civil war between rebels and the Manistani military. (Source: Wikipedia)
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