Only 3 ways to overcome this predicament

These are the only 3 ways that I see shin will be able to survive this.
Firstly shin and hi shin unit completely commit to siege they do everything to overpower the kantan soldiers on the top since it’s literally survival or there gonna die like Xiang yu did during the battle of julu where he destroyed the boats and cooking pots before engaging the army. From there they do a sai where they stay on the walls of kantan for as long as possible protecting themselves from both the interior and the outside. Zhao king gets pissed that the hi shin unit is on top of the walls and that riboku in his opinion is using his capital as fodder and he suspects and fears that riboku might sacrifice him and the people of kantan to win. If that’s the case he won’t care about keeping his throne as survival is more important similar to kakukai who already distrusts riboku and prevented renpa from coming back from Chu because they placed there survival over everything else even their positions. This is a stretch since shin is already facing the enemy so he’s essentially acting as the rearguard against the enemy whilst his soldiers are going up which could work but extremely risky. The hi shin unit might fight with all the strengths and get buffs seeing there captain fight to save their backs.

Secondly and this is the least likely practically impossible shin is able to fight with his forces and make a break through the enemy. Now this could be possible if they weren’t already sieging kantan and on ladders but being caught off guard like that makes this very low likelihood even if shin was able to kill riboku in a duel the hi shin unit will get annihilated.

Thirdly and this is the most likely is that mouten and kyoukai already anticipated the fact that most of the zhao army had managed to bypass them and they pushed for riboku to try to flank the hi shin unit so that they can perform their own flank on riboku. This would be a reverse sai where it would be like yotanwas forces were flanked by another massive army. This could work and I think it’s the most likely one. I would like to think shin didn’t just make a retarded move without even an instinctive insight in to the trap im hoping he’s acting to give riboku the impression that there is no reinforcement. Shin isn’t bad at keeping secrets he did keep the secret of the commanding general for gyou a secret even from his main boys for the sake of information blockade. The plan requires that shin and hi shin unit is caught completely off guard only way for riboku to completely commit all his forces for an attack I mean a situation like that is entirely hopeless.