Yep - Link has to be at 70% and you need to fight a battle in Yaksha for it to evolve.
In Pokémon Conquest, there is no evolution stone or evolution related item that you will need in order to evolve Eevee into Umbreon instead you will need to have at least a 70+% Link level and then you will need to head to the Kingdom that is called "Yaksa" and you will need to find something that you can accomplish there and then your Eevee will evolve to Umbreon.
To make Eevee evolve into an Umbreon, you have to level it up with high happiness at night.
Get the eevee to a 70% link and then battle with it in Yaksha.
Evolve it at 12 pm
Eevee doesn't have a set level to evolve into Umbreon. All you have to do to evolve it is max out its happiness at night. ~KKMG1
Eevee evolves to Umbreon when it has high happiness, and it levels up while it is dark.
You have to wait a while after you get to pick who evee will evolve into (umbreon) You have to wait a while after you get to pick who evee will evolve into (umbreon)
you can't, you have to max out eevee's happiness at night to evolve it into Umbreon.
Level it up at night
Moonstone
You can get an umbreon by getting an eevee from bill in goldenrod city (in a house) and then you can evolve eevee into umbreon by making it happy and leveling it up at night time.
you cant you must evolve an eeve at night with max friendship.