The Seattle Mariners are off to a sizzling 7-1 start, a surprise given their offseason revolved around loss. The Mariners traded mainstays James Paxton, Robinson Cano, Mike Zunino, and Edwin Diaz, and permitted slugger Nelson Cruz to leave through free agency. The winter may have been about the departed, but the spring has been about arrivals: Tim Beckham, Domingo Santana, and numerous other additions have contributed to the hot start.

For our money, Seattle's most interesting newcomer is left-handed starter Yusei Kikuchi, whom the M's lured from the Saitama Seibu Lions by guaranteeing him at least $56 million.

Kikuchi has started twice thus far for the Mariners, including rounding out their series in Tokyo, Japan against the Oakland Athletics. In 10 ⅔ innings, he's allowed three earned runs on eight hits and two homers and has struck out eight while walking one. It's too early to place much weight onto or thought into those numbers, but it has become apparent in the small sample at hand that Kikuchi's slider is the key to his success.

According to Statcast, Kikuchi threw 22 sliders his last time out, on Friday against the Boston Red Sox. He tossed nearly an even amount against lefties and righties and coerced a whiff on more than half the swings taken on the pitch, which features some hard, diving movement -- notable since his other offerings weren't nearly as effective at generating swings and misses. Kikuchi even demonstrated the ability to throw what's known as a back-foot slider against right-handed batters:

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Kikuchi's pitches and location versus right-handed batters Baseball Savant

Kikuchi's ability to consistently locate that pitch is important because he's going to need it in order to fend off right-handed batters. That may sound counterintuitive: typically, the slider is a pitch that's more effective versus same-handed hitters for obvious reasons -- it's easier to hit a pitch moving toward you than one moving away from you -- but mastering the back-foot slider is part of what has made pitchers like Chris Sale so effective during their careers.

Interestingly enough, Kikuchi has been on a quest to better implement his slider since consulting with an analytics firm. Jim Allen of Kyodo News wrote about the relationship, and what Kikuchi discovered. Here's part of what Kikuchi's consultant told Allen:

"In Japan, there is a sense that most batters are looking for fastballs rather than sliders. For that reason, we felt it's going to be harder to get swings and misses with your fastball, so he settled on improving his slider to get batters to miss it."

Whether Kikuchi's slider remains this effective at missing big-league bats is to be seen. He does have other things going for him, however, that should help him solidify himself as a mid-rotation starter -- including a 93 mph fastball, a curveball with better-than-average spin, and a highly deceptive delivery that sees his body shield the ball throughout. 

As such, the Mariners have reason to be optimistic so far -- about their season, and about their new southpaw.