Heine Istari

One of the invitees to Adra, the Castle of Separation.
He has the double elemental affinity of Fire and Water. His specialty in magecraft is “Change.”
For a human magus, he is in the strongest class of combat ability. A pure and noble “Knight.”
Furthermore, as was mentioned in the Kadokawa paperback edition, he mentions that the title of knight wasn’t given to him by “her Highness the Queen.” His reasoning for the use of “Her Highness” rather than “Her Majesty” is that, “someone who is only a member of an earthly royal family isn’t qualified for the highest title.” A very magus-like sentiment. At any rate, he has a background in France, and the character of one who was once a member of the Holy Church.
The fate he reached at the Castle of Separation could only be described as a result of coming up against the wrong opponent. An issue of compatibility, as is so often the case in Type Moon.
Taking care of Rosalind up until the very moment of his death, his wish was entrusted to Seigen. Though ultimately Seigen was the culprit behind the Adra case…even so, there was no betraying the wish of that knight.

Lord El-Melloi II Case Files material: Lord El-Melloi II Case Files Glossary