- Real Name: Chiba Masashi (千葉昌嗣)
- Nicknames: PSY, PESSY
- Birthday: December 27, 1976
- Birthplace: Tokyo, Japan
- Blood Type: B
- Height: 5.3 feet (162cm)
- Weight: 114.7 pounds (52kg)
- Job: MC
- Influences: New York Dolls, June Sky Walkers
- Favorite Artits: Debussy Debussy, Sakamoto Maaya
- Most Memorable Song: Zeek Roy-Z
- Special skills: Graphics, "Television Child" (一番テレビっ子)
PES is generally seen as the spirited & childish member of RIP SLYME. However his skills as a musician must not be overlooked. Being the only member other than FUMIYA who has composed singles for the group, he is a very important asset. Noted very much for his high, and at times, melodic voice, a not completely rare but unusual sound for Hip-Hop. However it is his singing voice that gives him an advantage and helped their song "ONE" be a big hit. In total he has written 3 singles for his group; "ONE", "Tasogare Surround" & "Hot Chocolate". He has as well played the guitar for some songs such as their Tekken 5 song "More & More" on the Good Job! album. Tomoyuki Tanaka from Fantastic Plastic Machine has praised PES' great sense of melody.
PES claims to have changed schools over 20 times and is unable to remember his birthplace. This creates him as a person of a different background. He never had a father, living only with his mother (who worked at an Esute) & grandmother. Attending a Japanese International School (where he met future member ILMARI), he quit after finishing middle school. He then took time pursuing things such as skateboarding, surfing & the guitar. Thinking he was quite good, PES aspired to be a professional surfer - until an Australian pro surfer visiting changed his mind (Now he goes surfing with group member SU). Juggling between music & skateboarding - he slowly got interested in Hip-Hop where ILMARI & RYO-Z strongly urged him to join.
His nickname was given by RYO-Z who claimed "You're small and cute, so you're Pes!". His hobbies include games & the popular anime Gundam, having written lyrics in one song inspired by the anime. He has a certain interest in graphics and has helped create backdrops for certain concerts.
He owns two pet chihuahuas, Giorgio & Joanna.