When you select to march on Tererra, Oichi appears to you and tells you that it’s time. She warns you that Terrera has many Ground-type Pokemon- and their warriors use a variety of other types too. She anticipates this being a tough fight.
Once you’ve launched your invading force, the game cuts to the gates of Terrera. Shingen and his Rhyperior are waiting there for you- he says that he’s heard rumors about you. Confidently, he asks why you’re here, and if you want to challenge him. The very idea gets a laugh out of him and his rhinoceros, and he ridicules the very idea.
Although a bit intimidated, Oichi backs you up, declaring that you’re ‘serious’ about your invasion attempt. Shingen actually acts a bit mollified, apologizing... and then saying that just the thought of it provokes amusement in him. He tells you that he’d be happy to do battle- if you were any kind of a match for him. He then qualifies that there is someone ‘here’- but doesn’t clarify what he’s implying, telling you to return when you’ve gotten tougher.
Oichi stammers in astonishment at this- and then you’re booted back to where you marched from.
You stand in your fortress, looking glum- and Oichi laments that the two of you are just standing around not making any further progress- meanwhile Nobunaga is continuing on his mission of conquest.... and then there’s a hubbub starting, as Terrera warriors march in a counter-attack!
It is Yukimura, Shingen’s second in command, who has come to lay siege to your fortress. He greets you formally, and introduces himself- then tells you that he’s present under orders from Shingen. He says it has something to do with your visit to Terrera: he is here to challenge you to combat!
Be careful here- being on the defensive means that you are going to take your actions second in each turn, rather than first as you’re accustomed to. Perhaps amusingly, Shingen’s forces really aren’t anything too big to worry about without the big warrior himself- all five of the Pokemon you’re going to face here are in their basic form, which means that only the Drillbur and Rhyhorn have particularly strong attacks, and the Rhyhorn is the only real defensive powerhouse, though Scraggy can take a bit of a beating.