Langrisser I Remastered - Part 12 - Chapter 12 - Twin Castle - Path C - Don't Defeat Sar Galious
3If you want to move on to path E, you have to not defeat Sar Galious, which is the hidden secondary objective of this.
If you defeat him before Digos you'll stay along this path, and won't get to see the betrayal.
Given this information, just place your strongest heroes on the right and ignore the left side for the most part. Rushing in is viable, but even with buffs my equivalent units were only on par with Digos'.
Use Lance's cavalry, and when buffed they'll tear through his soldiers.
Of course I used Ledin because I'm trying to get the trophy for maxing his jobs out (which of course I will get in this playthrough).
Digos does have a few surprises up his sleeves too. His wide range thunder attack can hurt, so you may want a healer on standby to mitigate what he can do.