There will be 3 lower Hosue by-elections on April 28th. Biden will visit Japan on April 10th. There is a path where Kishida calls a general election for April 28th gambling that pictures of him and Biden together in the Japanese press will push up his ratings to give him a chance at winning on April 28th. If he does not then he might face a slow death over the next couple of years before a likely LDP defeat when the general election does come.
By LDP defeat, do you mean a loss of a single party majority but retention of power or a loss of LDP-Komei rule over Japan entirely?