Suzuha at the party
Operation Eldhrimnir (can be written using 'í' too) was coined by Okabe in episode 10 for the plan to invite Suzuha to a party the following day, regardless of whether she meets her father or not. The party is meant to be a celebration if Suzuha meets her father, and a farewell party if she doesn't.
Namesake[]
Quoting user 'nhahtdh' from the website anime.stackexchange.com (improved text):
In Norse mythology, Eldhrímnir (Old Norse for "fire-sooty") is the cauldron in which the gods' cook, Andhrímnir, prepares Sæhrímnir every night.
Looking at the entry for Einherjar:[]
The einherjar (Old Norse for "single (or once) warrior") are those who have died in battle and are taken to Valhalla by the valkyries. In Valhalla, the einherjar feed on Sæhrímnir, the beast that resurrects every night, and are fed on mead (from the udder of the goat Heiðrún) by the valkyries.
And Sæhrímnir:[]
Sæhrímnir is the creature that is killed and eaten every night by the Æsir and the einherjar. The cook of the gods, Andhrímnir, is responsible for slaughtering Sæhrímnir and preparing it in the cauldron Eldhrímnir. After Sæhrímnir is eaten, the beast is brought back to life to provide food for the next day.
I hope I am not reading too much into this, but since Eldhrímnir is the cauldron used to cook food for the einherjar who have died in battle, it bears a resemblance to the fact that Suzuha introduces herself as a "warrior" and fails to meet her father the next day. Or perhaps the name simply refers to the feast, with all its food and drink, alluding to the fact that the cauldron is the cook who prepares a feast.