Hmm, as a growing W Len player myself, I'll say...
Disadventageous Matchups: Warcueid, Len, V Akiha, Nrvnqsr, Sion, Hisui, Kohaku
Stalemating Matchups: W Len, duh. (In the instance of a mirror match, turn your game off instantly.), Shiki, Nanaya, Ciel, Akiha, V Sion, Arcueid
Adventageous Matchups: Aoko, Mech Hisui, Warachia, Miyako, Kouma, Satsuki
Warcueid- Plain and simple, W Len's bnb doesn't work on her. Not to mention the fact that Warcueid is way more mobile than White Len, and her j.b keeps our favorite albino loli away. Disadvantage.
Len- Bnb don't work on her, either. Len's damage output is much higher, to boot.
V Akiha- V Akiha's speed is overwhelming for W Len, who is a snail. I find myself limited to using 214a in order to escape V Akiha's strong corner pressure, as well.
Nrvnqsr- His animals and range on attacks like 5b and 4c keep W Len away the whole match.
Sion- Higher damage, more range with 214a/b/c and 2c. Don't have much experience in this match up though.
Hisui- Super fast jump start plus oki setups that are hard to escape.
Kohaku- Oki madness and range advantage.
Aoko- W Len has a lot of orb dispelling options such as 236 a or b, 5b, 5c, j.2c, and j.[c]. Once you get knockdown in the corner, the match should pretty much be yours.
Mech Hisui- W Len's dash is an easy way to evade projectiles and punish Mech quickly.
Warachia- j.[c] can punish his attempts at zoning with j.b. He also takes quite a bit of damage, so I think this pushes W Len into the adventageous position.
Miyako- W Len's 236b works as a great anti-air on this fellow loli. Her dash is also an easy way to reverse Miyako's pressure and escape 236b crossover.
Kouma- Kouma can get hit by the ground throw combo. (Not everyone can be, iirc) He is slow like W Len, so going against someone with similar speed takes away a large disadvantage.
Satsuki- Satsuki can take extra hits in W Len's bnb. (you can successfully 2C after 2b, 623a into 5c 4b.) W Len is also just generally good against these physical characters.