Kodachi vs Scorcher is basically in favor of whoever is retreating at the time. The way you want to fight this matchup is to try to be retreating at as close to your maximum range as possible. Scorchers slightly outrange retreating Kodachis, so can do some small freeish damage there, but usually you will spend most of your time kiting them, and occasionally trying to dive into them to try and get close where your damage potential is high enough that a single scorcher can fry a single kodachi.

Note that a retreating scorcher will deal a relatively significant portion of its max damage to a chasing kodachi, because kodachis are fast enough to run into the projectile before its damage falls off completely. That makes scorchers suspiciously strong vs kodachi on the retreat compared to diving the kodachi, where you have to get fairly close to do any meaningful damage.

1 scorcher and 1 kodachi are very close to equivalent when skirmishing each other and scorchers are cheaper, so if you have an extra scorcher or two over their kodachi count, you're in a good position. You can either send your extra scorchers to harass their back line, or you can try to create outflanks where you can pincer the kodachis between your scorchers and force them to fight 2 vs 1 at a range where you can get most of your damage in.

Since the last update scorchers are faster than kodachis, so you have the luxury of escaping a combat that doesn't favor you, whereas the kodachi player does not. Try to play 1 scorcher vs 1 kodachi in the early game, and just keep your scorchers in between his kodachis and your base. When you have enough breathing room to make fencers, deploying fencers in defensive positions or just poking at their kodachis will force them to find ways to make trades with you to keep from getting pinned down in their corner of the map. Stay mobile, and cover your fencers with scorchers/rippers.