This tome is suitably named “Nosferatu” for its vampiric effect of absorbing HP from an enemy unit. It is especially unique in Gaiden, as it is the only weapon (apart from the Falchion and certain Amiibo weapons) that can damage Duma after his HP has been depleted to 52.
In Mystery of the Emblem and its remake, this spell may only be cast by female magic users.
In Fire Emblem: Genealogy of the Holy War, Nosferatu can only be obtained in Chapter 6, during the second generation. In order to obtain it, Seliph must capture Isaach Castle before capturing Sophara castle, and must speak to Julia, after which she will obtain the Nosferatu, an A-Rank tome. Thanks to her major Naga blood, Julia is the only character who has access to Nosferatu and can wield it. (Theoretically, Deirdre can wield Nosferatu for the same reason Julia can, but the tome is not available in the first generation.) Conversely, if Sophara Castle is captured first, Seliph will give Julia the Aura tome, and Nosferatu will no longer be available for the rest of the game.
In The Sacred Stones, the Nosferatu tome is not available for purchase in any stores on the World Map, essentially meaning that only a few obtainable copies of the tome exist in any one given gameplay. Knoll joins the player's army with the tome as a starting item, and there is at least one available in a certain chest residing within the Tower of Valni. Furthermore, the shop at Narube River also offers this tome for sale when a battle takes place there, other than skirmishes in Creature Campaign.
Nosferatu traps an enemy directly in front of Robin, dealing damage while healing them. Robin will always deal 15% damage, however, depending where Robin hits his opponent, the healing changes. If attacking from the front, Nosferatu will heal 13% of Robin's damage. If attacking from behind, Robin will heal 16% of their damage. Nosferatu is considered a grab move and can hit through shields. It has a maximum usage of 4 casts before Robin is forced to discard it. A new tome will regenerate after 40 seconds.
The damage healed is mainly based upon percentage differences. If the enemy has 0% and Robin is at 999%, Robin will heal themselves by 300%, when Robin has 160% and the enemy has 0%, Nosferatu will heal Robin by 60%.
"Resire" is most likely a reference to "resile", a word which means to "draw back" and "recoil". Its English name, "Nosferatu", is a Romanian word that is synonymous with "vampire", popularized by an unlicensed film adaption of Dracula which replaced, among other names, "Dracula" with "Nosferatu".
When this spell is cast on a wall or any other non-living obstacle, the wielder will still be able to leech HP from it. This can prove to be rather useful as such objects tend to lack resistance, thus returning the maximum amount of HP to the caster in question. (This is not true in Fates)
In Genealogy, Nosferatu uses the same animation as using the Earth Sword at long range. They also share the same life-steal effect.
In Fire Emblem Warriors Nosferatu produces light effects when used by Linde and dark effects when used by Tharja during their Awakening and Warrior Specials, referrencing how the spell is classified in their respective games.