On 6/11, there will be skill buffs given to a lot of gacha 6* and rarity grown 6* characters. These may change when the maintenance actually passes over. If so, I will update this list.

RG = Rarity Grown for short.

All target skills
RG 5* Cosmos
Multiplier: 2.0x -> 2.7x
Level 1 Rate: 30% -> 32%
Level 5 Rate: 40% -> 42%

6* Tall Stewartia / Himeshara (Christmas)
Multiplier: 2.1x -> 2.8x
Level 1 Rate: 24% -> 27%
Level 5 Rate: 34% -> 37%

6* Cacao
Multiplier: 2.1x -> 2.8x
Level 1 Rate: 27% -> 27%
Level 5 Rate: 37% -> 37%

RG 5* Lavender
Multiplier: 2.2x -> 2.8x
Level 1 Rate: 24% -> 27%
Level 5 Rate: 27% -> 37%

All of these 6*s:
6* Ivy (New Year)
6* Acacia
6* Apricot
6* Ionocidium
6* Ixia
6* Evergreen Candytuft
6* Hare's Tail Grass
6* Scotch Broom
6* Epidendrum (Swimsuit)
6* Royal Water Lily (June Bride)
6* Golden Lace
6* Dancing Lady Orchid (Bride of Fos)
6* Aizoon Stonecrop
6* Wolf Berry
6* Curcuma
6* Wheat
6* Saffron
6* Herbaceous Peony
6* Herbaceous Peony (Halloween)
6* Soapwort
6* Wax Vine
6* Japanese Anemone
6* Stock
6* Snow Drop
6* Sparaxis
6* Blushing Bride
6* Hollyhock
6* Azalea
6* Burning Bush
6* Bush Clover
6* Lotus
6* Ghost Weed
6* Tree of a Thousand Stars
6* Viola
6* Viola (Yukata)
6* Red Spider Lily
6* Red Spider Lily (World's Flower Shrine Maiden)
6* Pygmy Water Lily
6* Loquat
6* Black Baccara
6* Freesia
6* Summer Squash
6* Sneezeweed
6* Purslane
6* Easter Cactus
6* Horse Chestnut
6* Coral Bush
6* Mimosa
6* Maple
6* Mistletoe
6* Apple (Tanabata)
6* Camellia Wabisuke
RG 5* Azuki Bean
RG 5* Anemone (World's Flower Shrine Maiden)
RG 5* Tiger Lily
RG 5* Rough Potato
RG 5* Sawagikyou
RG 5* Cyclamen (Radiant Princess)
RG 5* Showy Evening Primrose (Easter)
RG 5* Toad Lily
RG 5* Laurentia (Ninja)

Multiplier: 2.2x -> 2.8x
Level 1 Rate: 24% -> 27%
Level 5 Rate: 34% -> 37%

6* Royal Water Lily / Ooonibasu
Multiplier: 2.3x -> 2.9x
Level 1 Rate: 22% -> 24%
Level 5 Rate: 34% -> 34%

6* Christmas Rose
Multiplier: 2.3x -> 2.9x
Level 1 Rate: 24% -> 24%
Level 5 Rate: 34% -> 34%

6* Nightmaher
6* Habranthus
Multiplier: 2.4x -> 2.9x
Level 1 Rate: 22% -> 24%
Level 5 Rate: 32% -> 34%

6* Dendrobium
6* Cattleya
6* Cattelya (Radiant Princess)
6* Chocolate Lily / Kuroyuri
6* Nadeshiko / Pink
6* Nerine
Multiplier: 2.4x -> 2.9x
Level 1 Rate: 24% -> 24%
Level 5 Rate: 34% -> 34%

Skills with damage based on remaining enemies
6* Pink Ladies
6* Reeves Spirea (Easter)
6* Dusty Miller (Christmas)
6* Japanese Silver Grass (Swimsuit)
6* Paphiopedilum
6* Sneezeweed (Easter)
RG 5* King Protea
RG 5* Pickerel Weed

Multiplier vs. 1 target: 4.7x -> 4.7x
Multiplier vs. 2 targets: 2.7x -> 2.8x
Multiplier vs. 3 targets: 2.0x -> 2.2x
Level 1 Rate: 27% -> 27%
Level 5 Rate: 37% -> 37%

Two target skills
6* Daisy
Multiplier: 2.4x -> 3.6x
Level 1 Rate: 30% -> 30%
Level 5 Rate: 40% -> 40%

6* Dogwood / Hanamizuki
RG 5* Blood Iris
RG 5* Edelweiss
RG 5* Marvel of Peru
RG 5* Spoon Wood
RG 5* Pot Marigold
RG 5* Heart Vine
RG 5* Quince
RG 5* Coral Bush (June Bride)
RG 4* Japanese Cypress
RG 4* White Tulip
RG 2* Cyclamen
RG 2* Purple Pansy
Multiplier: 3.0x -> 3.8x
Level 1 Rate: 20% -> 24%
Level 5 Rate: 30% -> 34%

Single target skills
6* Cactus / Saboten
Multiplier: 4.0x -> 5.0x
Level 1 Rate: 36% -> 36%
Level 5 Rate: 46% -> 46%

RG 3* Alstromeria
Multiplier: 4.6x -> 5.4x
Level 1 Rate: 28% -> 28%
Level 5 Rate: 38% -> 38%

6* Peach Blossom / Hanamomo
Multiplier: 4.2x~4.8x -> 5.0~5.4x
Level 1 Rate: 28% -> 28%
Level 5 Rate: 38% -> 38%

6* Trailing Abutilon (Athletic Meet)
6* Japanese Apricot
6* Sakura
6* Daisy (Halloween)
RG 5* Spring Starflower
RG 5* China Root
RG 5* Tachibana
RG 5* Golden-rayed Lily
RG 5* Moonflower
RG 3* Moth Orchid
Multiplier: 5.2x -> 5.4x
Level 1 Rate: 26% -> 28%
Level 5 Rate: 36% -> 38%

Single target, HP suction skills
RG 5* Dalmation Bellflower / Otomegikyou
Multiplier: 3.7x -> 4.1x
Level 1 Rate: 28% -> 32%
Level 5 Rate: 38% -> 42%

RG 5* Water Lily / Suiren
Multiplier: 3.8x -> 4.1x
Level 1 Rate: 32% -> 32%
Level 5 Rate: 42% -> 42%

RG 5* Anemone (Radiant Princess)
RG 5* Delphinium (Athletic Meet)
RG 5* Squirrel Tail Grass
Multiplier: 4.1x -> 4.3x
Level 1 Rate: 28% -> 28%
Level 5 Rate: 38% -> 38%

6* Kerria
6* Red Ginger
RG 5* Adenium
RG 5* Dancing Lady Orchid
RG 5* Easter Lily
RG 5* Aconite
RG 5* Rainbow Rose
RG 4* Turnip Rape
RG 4* African Violet
Multiplier: 4.3x -> 4.3x
Level 1 Rate: 26% -> 28%
Level 5 Rate: 36% -> 38%